docs/ci: automate CHANGELOG updates and retroactively document post-v0.5.0 changes

- Fix semantic-release autoescape=true Jinja2 bug preventing CHANGELOG generation
- Add explicit changelog_file, mode=update, output_format=md to pyproject.toml
- Add fallback semantic-release changelog step in release.yml
- Manually true up CHANGELOG.md with comprehensive v0.40.0 retroactive entry covering
  all post-v0.5.0 additions: security middleware, 6 new storage providers, PDF processing
  improvements, dual-table status tracking, notification system, admin file manager,
  browser extension v1.1, path traversal fixes, and documentation additions
- Add Documentation-First Development section to CONTRIBUTING.md and AGENTIC_CODING.md
- Fix README.md quick-start commands and screenshots note
- Update TODO.md to reflect current version and completed tasks"

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

AGENTIC_CODING.md

@@ -71,6 +71,22 @@ DocuElevate/
    - Ensure you understand the Celery task flow
    - Consider impact on database schema
 
+### Documentation-First Principle
+
+**Documentation is as important as tests and code.** Every change must include documentation updates in the same commit/PR.
+
+| Change type | What to update |
+|-------------|---------------|
+| New feature | `docs/UserGuide.md`, `docs/API.md` (if API), `docs/ConfigurationGuide.md` (if config) |
+| New config option | `docs/ConfigurationGuide.md` and `.env.demo` |
+| New API endpoint | `docs/API.md` |
+| Bug fix (user-visible) | `docs/Troubleshooting.md` |
+| Deployment change | `docs/DeploymentGuide.md` |
+| Security change | `SECURITY_AUDIT.md` |
+| Breaking change | CHANGELOG (auto-generated) + migration notes in relevant docs |
+
+**Never edit `CHANGELOG.md` or `VERSION` manually.** These are managed automatically by `python-semantic-release` on every merge to `main`.
+
 ### Code Conventions
 
 #### Python Style