chore: update docs and redesign landing page hero
- CLAUDE.md: correct Docker container names, update migration format
docs (hash IDs now default), fix Node path in Lesson 63, update
design system values to electric blue accent, add retracted lessons
note, add GitNexus section
- .gitignore: add .gitnexus
- Landing page: replace animated chat preview with ticket-comparison
hero layout; remove backdrop-filter from scrolled nav (aligns with
design system); clean up removed chat animation CSS
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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