Add CI/CD workflows and security policy

.github/CI_CD_PRIMER.md

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+# CI/CD Primer for Stegasoo
+
+## What is CI/CD?
+
+**CI** = Continuous Integration
+**CD** = Continuous Deployment
+
+Think of it as a robot assistant that automatically:
+1. **Tests your code** every time you push
+2. **Checks formatting** so code stays consistent
+3. **Publishes releases** when you tag a version
+
+```
+You push code → GitHub runs workflows → You get ✓ or ✗
+```
+
+---
+
+## How It Works
+
+### The Trigger
+
+When you `git push` or create a Pull Request, GitHub looks for workflow files in:
+```
+.github/workflows/*.yml
+```
+
+Each `.yml` file defines a workflow - a series of steps to run.
+
+### The Runners
+
+GitHub provides free Linux/Mac/Windows VMs that:
+1. Clone your repo
+2. Set up Python
+3. Run your commands
+4. Report success/failure
+
+You don't manage servers - GitHub does.
+
+---
+
+## Your Workflows
+
+### 1. `test.yml` - Run Tests on Every Push
+
+**When it runs:** Every push, every PR
+
+**What it does:**
+```
+1. Spins up Ubuntu VM
+2. Installs Python 3.10, 3.11, 3.12
+3. Installs your package + dependencies
+4. Runs pytest
+5. Reports pass/fail
+```
+
+**You'll see:** Green ✓ or red ✗ on your commits
+
+### 2. `lint.yml` - Check Code Style
+
+**When it runs:** Every push, every PR
+
+**What it does:**
+```
+1. Runs ruff (fast Python linter)
+2. Checks black formatting
+3. Fails if code isn't formatted
+```
+
+**Why:** Keeps code consistent, catches common bugs
+
+### 3. `release.yml` - Publish to PyPI
+
+**When it runs:** Only when you create a version tag
+
+**What it does:**
+```
+1. Builds the package (wheel + sdist)
+2. Uploads to PyPI
+```
+
+**You trigger it by:**
+```bash
+git tag v2.2.0
+git push origin v2.2.0
+```
+
+---
+
+## Day-to-Day Usage
+
+### Normal Development
+
+```bash
+# Make changes
+git add .
+git commit -m "Add new feature"
+git push
+```
+
+Then check GitHub → Actions tab → See if tests pass.
+
+### If Tests Fail
+
+1. Click the failed workflow
+2. Click the failed job
+3. Read the error log
+4. Fix locally, push again
+
+### Making a Release
+
+```bash
+# 1. Update version in pyproject.toml and constants.py
+# 2. Commit the version bump
+git add .
+git commit -m "Bump version to 2.2.1"
+git push
+
+# 3. Create and push a tag
+git tag v2.2.1
+git push origin v2.2.1
+
+# 4. GitHub automatically publishes to PyPI
+```
+
+---
+
+## Reading the GitHub UI
+
+### Actions Tab
+
+```
+Repository → Actions → [List of workflow runs]
+```
+
+Each run shows:
+- ✓ Green checkmark = passed
+- ✗ Red X = failed
+- 🟡 Yellow dot = running
+
+### Pull Request Checks
+
+When you open a PR, you'll see:
+```
+┌─────────────────────────────────────────┐
+│ All checks have passed                  │
+│ ✓ test (3.10) — 45s                     │
+│ ✓ test (3.11) — 42s                     │
+│ ✓ test (3.12) — 44s                     │
+│ ✓ lint — 12s                            │
+└─────────────────────────────────────────┘
+```
+
+---
+
+## Setting Up PyPI Publishing
+
+For `release.yml` to work, you need to add a PyPI API token:
+
+### One-Time Setup
+
+1. **Create PyPI account** at https://pypi.org/account/register/
+
+2. **Generate API token:**
+   - PyPI → Account Settings → API tokens
+   - Create token (scope: entire account or just stegasoo)
+   - Copy the token (starts with `pypi-`)
+
+3. **Add to GitHub:**
+   - GitHub repo → Settings → Secrets and variables → Actions
+   - New repository secret
+   - Name: `PYPI_API_TOKEN`
+   - Value: paste the token
+
+Now `release.yml` can publish automatically.
+
+---
+
+## Common Scenarios
+
+### "Tests pass locally but fail in CI"
+
+Usually means:
+- Missing dependency in `pyproject.toml`
+- Hardcoded path that doesn't exist in CI
+- Test relies on local file
+
+### "Lint is failing"
+
+Run locally to see/fix:
+```bash
+# Check issues
+ruff check src/
+
+# Auto-fix what's possible
+ruff check --fix src/
+
+# Format code
+black src/
+```
+
+### "I want to skip CI for a commit"
+
+Add `[skip ci]` to commit message:
+```bash
+git commit -m "Update README [skip ci]"
+```
+
+---
+
+## Costs
+
+GitHub Actions is **free** for public repos.
+
+For private repos: 2,000 minutes/month free, then paid.
+
+---
+
+## Summary
+
+| Action | What Happens |
+|--------|--------------|
+| `git push` | Tests + lint run automatically |
+| Open PR | Tests must pass before merge |
+| `git tag v*` | Publishes to PyPI |
+| Check results | GitHub → Actions tab |
+
+That's it! Push code, check for green checkmarks.

.github/workflows/lint.yml

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+# Check code style and formatting
+name: Lint
+
+on:
+  push:
+    branches: [main, master, develop]
+  pull_request:
+    branches: [main, master, develop]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    
+    steps:
+      # 1. Get the code
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      # 2. Set up Python
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      # 3. Install linting tools
+      - name: Install linters
+        run: |
+          python -m pip install --upgrade pip
+          pip install ruff black
+      
+      # 4. Run ruff (fast linter - catches bugs and style issues)
+      - name: Run ruff
+        run: |
+          ruff check src/ tests/ frontends/
+      
+      # 5. Check black formatting (doesn't modify, just checks)
+      - name: Check black formatting
+        run: |
+          black --check src/ tests/ frontends/
+
+  # Type checking (optional but helpful)
+  typecheck:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+          pip install mypy
+      
+      - name: Run mypy
+        run: |
+          mypy src/stegasoo --ignore-missing-imports
+        continue-on-error: true  # Don't fail build on type errors (yet)

.github/workflows/release.yml

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+# Publish to PyPI when a version tag is pushed
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'  # Triggers on v1.0.0, v2.1.0, etc.
+
+jobs:
+  # First, run tests to make sure everything works
+  test:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libzbar0
+      
+      - name: Install package
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+      
+      - name: Run tests
+        run: pytest
+
+  # Then build and publish
+  publish:
+    needs: test  # Only run if tests pass
+    runs-on: ubuntu-latest
+    
+    # Required for PyPI trusted publishing (recommended)
+    permissions:
+      id-token: write
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install build tools
+        run: |
+          python -m pip install --upgrade pip
+          pip install build twine
+      
+      - name: Build package
+        run: python -m build
+      
+      - name: Check package
+        run: twine check dist/*
+      
+      # Option 1: Trusted Publishing (recommended, no token needed)
+      # Set this up at: https://pypi.org/manage/project/stegasoo/settings/publishing/
+      - name: Publish to PyPI (Trusted Publishing)
+        uses: pypa/gh-action-pypi-publish@release/v1
+        # No token needed if you configure trusted publishing on PyPI
+      
+      # Option 2: API Token (uncomment if not using trusted publishing)
+      # - name: Publish to PyPI (API Token)
+      #   env:
+      #     TWINE_USERNAME: __token__
+      #     TWINE_PASSWORD: ${{ secrets.PYPI_API_TOKEN }}
+      #   run: twine upload dist/*
+
+  # Create GitHub Release with changelog
+  github-release:
+    needs: publish
+    runs-on: ubuntu-latest
+    
+    permissions:
+      contents: write  # Needed to create releases
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v1
+        with:
+          generate_release_notes: true
+          files: |
+            dist/*

.github/workflows/test.yml

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+# Run tests on every push and pull request
+name: Tests
+
+on:
+  push:
+    branches: [main, master, develop]
+  pull_request:
+    branches: [main, master, develop]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    
+    strategy:
+      fail-fast: false  # Don't cancel other jobs if one fails
+      matrix:
+        python-version: ["3.10", "3.11", "3.12"]
+    
+    steps:
+      # 1. Get the code
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      # 2. Set up Python
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      
+      # 3. Install system dependencies (for pyzbar QR reading)
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libzbar0
+      
+      # 4. Install the package with all dependencies
+      - name: Install package
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+      
+      # 5. Run tests with coverage
+      - name: Run tests
+        run: |
+          pytest --cov=stegasoo --cov-report=xml --cov-report=term-missing
+      
+      # 6. Upload coverage report (optional - integrates with codecov.io)
+      - name: Upload coverage
+        uses: codecov/codecov-action@v4
+        if: matrix.python-version == '3.11'  # Only upload once
+        with:
+          files: ./coverage.xml
+          fail_ci_if_error: false  # Don't fail if codecov is down