feat(review): raise the RAG per-repo chunk cap from 1500 to 4000

[JSONbored]

Summary

• MAX_CHUNKS_PER_REPO (the hard per-repo bound on stored RAG vectors) raised from 1500 to 4000.
• All 3 currently-gated repos (gittensory, metagraphed, awesome-claude) were sitting exactly at the old cap, confirmed live — meaning real, indexable code was silently never making it into the RAG index for at least one of them.
• Storage/search cost at this scale is trivial for Qdrant regardless of cap size — the bound exists to protect against a future pathological repo, not because a few thousand vectors is expensive. The real cost of a higher cap is embedding compute, which perf(rag): cache chunk embeddings by content hash, skip redundant re-embeds #4365 (the blob-SHA skip-cache) turns from a recurring per-cron-cycle cost into a one-time cost per file.

Scope

• Stayed within wantedPaths (src/)
• No secrets/wallets/trust-score/reward values anywhere
• No changes to site/, CNAME, **/lovable/**, or CHANGELOG.md

Validation

• npm run typecheck
• npx vitest run test/unit/rag.test.ts test/unit/rag-index.test.ts — 127/127 passing (every cap-related test references the exported constant, none hardcode the old value)
• npm run db:schema-drift:check / npm run selfhost:env-reference:check — clean (no schema/env surface touched)
• npm audit --audit-level=moderate — 0 vulnerabilities

Safety

• No secrets/tokens anywhere
• Single-constant change, no logic touched

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.96%. Comparing base (ca5576f) to head (d08ddc0).
⚠️ Report is 7 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4398   +/-   ##
=======================================
  Coverage   93.96%   93.96%           
=======================================
  Files         401      401           
  Lines       36869    36869           
  Branches    13480    13480           
=======================================
  Hits        34644    34644           
  Misses       1569     1569           
  Partials      656      656           

Files with missing lines	Coverage Δ
src/review/rag.ts	100.00% <100.00%> (ø)

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