feat(review): add a combined "Copy for AI agents" block to the PR comment

[JSONbored]

Summary

Researched CodeRabbit's actual "Prompt for AI Agents" feature design (their own blog/docs + third-party extraction tooling) and adapted the pattern to gittensory's existing panel structure:

• Right after "Why this is blocked" / "Concerns raised", the comment now renders one collapsible titled "📋 Copy for AI agents" containing every blocker rewritten as a numbered instruction inside a single fenced plain-text code block.
• GitHub renders a copy icon on every fenced code block natively — no custom JS/UI needed.
• Matches CodeRabbit's newer design specifically (their own docs: they moved from one prompt per finding to ONE combined prompt per review, "to cut the repeated copy-paste this produced").
• Uses the full (pre-display-truncation) blocker set, not the human-facing capped subset shown in the bullets above it — an AI agent benefits from complete context even when the human-readable list is capped for scannability.
• Not gated by comment_verbosity: quiet — it's an extension of the blockers themselves (which are never gated), not decorative detail like Nits.

Test plan

• npm run typecheck — clean
• New dedicated test suite ('Copy for AI agents' block describe block in unified-comment.test.ts): omitted with no blockers, renders every blocker as a numbered item, uses the full (not truncated) blocker set, survives quiet verbosity, renders pre-expanded under detailed verbosity, escapes angle brackets consistently with every other public field
• Updated 5 pre-existing tests that asserted a blocker's text appears "exactly once" — now legitimately twice (once in "Why this is blocked", once in the new block); each updated assertion still separately confirms the text is never also restated under "Suggested Action" (the actual feat(miner): add schema-version migration runner across local stores #5347 regression this file already guards)
• npx vitest run across all 14 affected test files (unified-comment*, every *-collapsible.test.ts, all 5 queue*.test.ts) — 940/940 passing
• npm run test:engine-parity — clean
• Coverage: src/review/unified-comment.ts diff is 100% lines / 100% branches (verified via lcov; the two remaining uncovered items in this file are pre-existing, outside this diff's changed lines)

[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 94.40%. Comparing base (56d901d) to head (d82c449).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5387      +/-   ##
==========================================
- Coverage   94.43%   94.40%   -0.04%     
==========================================
  Files         551      551              
  Lines       44223    44227       +4     
  Branches    14654    14654              
==========================================
- Hits        41764    41751      -13     
- Misses       1784     1801      +17     
  Partials      675      675              

Flag	Coverage Δ
shard-1	43.80% <100.00%> (-0.37%)	⬇️
shard-2	34.08% <100.00%> (-0.50%)	⬇️
shard-3	32.18% <0.00%> (+0.64%)	⬆️
shard-4	31.30% <100.00%> (+0.02%)	⬆️
shard-5	33.12% <0.00%> (-0.21%)	⬇️
shard-6	43.58% <0.00%> (+0.20%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/review/unified-comment.ts	99.58% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

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