docs: refactor README to highlight auto-documentation feature

Simplified and restructured README with humble, straightforward tone:

- Lead with closed-loop feature (rebuild → auto-documentation → AI knowledge)
- Personal narrative ("built over 6 months") instead of academic framing
- Collapsible sections for detailed content (540 lines vs 993)
- Added Claude Code and Home Manager badges
- Created VHS demo script for rebuild process
- Added planning docs (CORE_THESIS, REFACTORING_PLAN, STRATEGY)

Benefits:
- More discoverable (clear value proposition above fold)
- Better GitHub presentation (topics, description, badges)
- Easier to understand (quick start prominent, details hidden)
- Maintains all existing content (just reorganized)

Related:
- GitHub description updated
- Topics added: nixos, claude-code, ai-tools, modern-cli
- docs/THE_CLOSED_LOOP.md explains technical implementation

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

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

Author: jacopone