Improve reservations and built-in documentation

[Aedalus]

• Improve reservation calendar behavior for authenticated users and filter the admin calendar to currently reservable equipment while retaining history.
• Add a reservations guide with Slack screenshots and expose it in both built-in and MkDocs navigation.
• Add generated documentation tables of contents, debug-mode cache bypassing, and responsive help-site styling.
• Navbar now turns green when local.
• Expand reservation and documentation test coverage.
• Pinned the CI version of ruff to match out requirements.txt. Seems out of date, but don't want to add a lot of lint fixes to an already cluttered PR.
• Bump version to v0.20.0

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.