Add professional project structure and documentation

New files:
- LICENSE (MIT) - Required legal file
- CHANGELOG.md - Version history following Keep a Changelog
- CONTRIBUTING.md - Contributor guidelines
- CODE_OF_CONDUCT.md - Community standards
- .github/ISSUE_TEMPLATE/ - Bug report and feature request forms
- .github/PULL_REQUEST_TEMPLATE.md - PR checklist
- src/stegasoo/py.typed - PEP 561 type hint marker
- examples/ - Usage examples (basic, file embedding, channel keys)

Updated:
- README.md - Added CI status badges

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -0,0 +1,165 @@
+# Contributing to Stegasoo
+
+Thank you for your interest in contributing to Stegasoo! This document provides guidelines and information for contributors.
+
+## Getting Started
+
+### Prerequisites
+
+- Python 3.10 or higher
+- Git
+- Docker (optional, for container testing)
+
+### Development Setup
+
+1. **Clone the repository**
+   ```bash
+   git clone https://github.com/adlee-was-taken/stegasoo.git
+   cd stegasoo
+   ```
+
+2. **Create a virtual environment**
+   ```bash
+   python -m venv venv
+   source venv/bin/activate  # On Windows: venv\Scripts\activate
+   ```
+
+3. **Install development dependencies**
+   ```bash
+   pip install -e ".[dev]"
+   ```
+
+4. **Install pre-commit hooks**
+   ```bash
+   pre-commit install
+   ```
+
+## Development Workflow
+
+### Code Style
+
+We use the following tools to maintain code quality:
+
+- **Black** - Code formatting (line length: 100)
+- **Ruff** - Linting
+- **MyPy** - Type checking
+
+Run all checks before committing:
+```bash
+black src/ tests/ frontends/
+ruff check src/ tests/ frontends/
+mypy src/
+```
+
+### Running Tests
+
+```bash
+# Run all tests
+pytest
+
+# Run with coverage
+pytest --cov=stegasoo --cov-report=term-missing
+
+# Run specific test file
+pytest tests/test_stegasoo.py
+```
+
+### Type Hints
+
+All new code should include type hints:
+
+```python
+def encode_message(
+    message: str,
+    carrier_image: bytes,
+    passphrase: str,
+    pin: str = "",
+) -> EncodeResult:
+    ...
+```
+
+## Making Changes
+
+### Branch Naming
+
+- `feature/description` - New features
+- `fix/description` - Bug fixes
+- `docs/description` - Documentation updates
+- `refactor/description` - Code refactoring
+
+### Commit Messages
+
+Write clear, concise commit messages:
+
+```
+Add channel key validation for private messaging
+
+- Implement validate_channel_key() function
+- Add tests for valid/invalid key formats
+- Update CLI to support --channel-key flag
+```
+
+### Pull Request Process
+
+1. **Create a feature branch** from `main`
+2. **Make your changes** with appropriate tests
+3. **Ensure all checks pass** (tests, linting, formatting)
+4. **Submit a PR** with a clear description
+5. **Address review feedback** promptly
+
+### PR Checklist
+
+- [ ] Tests added/updated for changes
+- [ ] Documentation updated if needed
+- [ ] CHANGELOG.md updated for user-facing changes
+- [ ] All CI checks passing
+- [ ] No merge conflicts with `main`
+
+## Project Structure
+
+```
+stegasoo/
+├── src/stegasoo/       # Core library
+│   ├── crypto.py       # Encryption/decryption
+│   ├── steganography.py # LSB embedding
+│   ├── dct_steganography.py # DCT embedding
+│   └── ...
+├── frontends/
+│   ├── cli/            # Command-line interface
+│   ├── web/            # Flask web UI
+│   └── api/            # FastAPI REST API
+├── tests/              # Test suite
+└── examples/           # Usage examples
+```
+
+## Reporting Issues
+
+### Bug Reports
+
+Please include:
+- Python version and OS
+- Stegasoo version (`stegasoo --version`)
+- Minimal reproduction steps
+- Expected vs actual behavior
+- Error messages/tracebacks
+
+### Feature Requests
+
+Please include:
+- Use case description
+- Proposed solution (if any)
+- Alternatives considered
+
+## Security
+
+If you discover a security vulnerability, please see [SECURITY.md](SECURITY.md) for responsible disclosure guidelines. **Do not open a public issue for security vulnerabilities.**
+
+## License
+
+By contributing, you agree that your contributions will be licensed under the MIT License.
+
+## Questions?
+
+Feel free to open a discussion or issue if you have questions about contributing.
+
+Thank you for helping make Stegasoo better!