chore: remove deprecated eval infra and update docs with new eval results

[BYK]

Summary

Removes ~10MB of dead eval infrastructure and updates website/README with context retention results.

Cleanup

Item	Size	Reason
auto-mem0.ts	295 lines	Dead code — never imported, Python sidecar bridge unreachable
cost-verifier.ts	268 lines	Dead code — never imported, only referenced in string literals
fixtures/recorded-responses/	2.0 MB (23 files)	Old v1 fixtures, superseded by v3
fixtures/recorded-responses-full/	7.8 MB (16 files)	Old v2 fixtures, superseded by v3
fixtures/projects/	17 files	Unreferenced fake project trees
fixtures/sessions/	4 empty dirs	Vestigial from earlier design
auto-mem0 references	~10 locations	Removed from types.ts, scenario files, CLI help

Docs Updates

Website (docs/index.html)

• Replace "19x Compression" chip with "400K+ Token Sessions"
• Update hero stats: +50% vs tail-window, 4.8/5.0 detail retention

README

• Add context retention results table (Lore 3.9 vs tail-window 2.6 at 400K)
• Update eval suite description (16 scenarios, 5 dimensions)
• Update v5 changelog