Phase 8: cleanup + polish

[CalebisGross]

Part of #339

Final phase:

• Remove all dead CSS/JS/HTML from monolith
• Final index.html is ~80 lines
• Delete Mind/Graph frontend code (keep API route for potential future use)
• Responsive pass (640px breakpoint)
• Theme verification across all 5 themes
• Performance: zero external requests in DevTools Network tab
• Run full 23-item functionality checklist
• Archive old mockups to internal/web/mockups/archive/

[CalebisGross]

In progress. 69 dead CSS rules removed (-8.2KB), old .tl-card layout CSS removed, mind view code removed. Remaining: more dead CSS cleanup, responsive pass, theme verification, performance check.