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>

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: true
+contact_links:
+  - name: Security Vulnerability
+    url: https://github.com/adlee-was-taken/stegasoo/security/advisories/new
+    about: Report security vulnerabilities privately
+  - name: Documentation
+    url: https://github.com/adlee-was-taken/stegasoo#readme
+    about: Check the documentation before opening an issue