fix(review): stop the Code review row contradicting itself when AI never ran

[JSONbored]

Summary

• Fixes a real UX bug found while investigating metagraphed PR test(selfhost): add unit-test seam for validate-selfhost-sourcemap #7491: when AI review never runs at all (e.g. a concurrent duplicate pass defers) but a deterministic gate blocker is still present (buildDualReviewNotes's FIX D1 deliberately folds gate blockers into the same list), the unified comment rendered a self-contradictory "1 blocker (No AI review summary)" line — reading as an AI pass that silently found something, when actually AI review never ran and something else entirely is blocking the PR.
• codeReviewRow now says so plainly: "1 blocker (no AI review ran — blocker is from a non-AI gate check)" when reviewerCount is 0 and a blocker is present. The zero-blocker case ("No blockers (No AI review summary)") is unchanged.

Scope

• Single function + its doc comment, plus tests. No behavior change to the gate's actual merge/close decision — this only fixes what the comment says about it.

Validation

• npm run typecheck
• npx vitest run test/unit/unified-comment.test.ts — 105 passed (2 new)
• Coverage check confirmed zero uncovered statements/branches in the changed function; no existing test asserted the old contradictory string, so nothing broke.

Notes

• Third follow-up from the same investigation as fix(review): stop large-registry-PR false-closes across grounding, content-lane, and issue matching #7931/test(review): cover the null-issue-title branch in the deliverable check #7940 — spawned as a background-task suggestion originally, fixed directly instead.

[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 89.12%. Comparing base (4482d47) to head (a390bf1).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7946      +/-   ##
==========================================
- Coverage   91.83%   89.12%   -2.71%     
==========================================
  Files         735       91     -644     
  Lines       75433    21762   -53671     
  Branches    22950     3819   -19131     
==========================================
- Hits        69272    19396   -49876     
+ Misses       5083     2187    -2896     
+ Partials     1078      179     -899     

Flag	Coverage Δ
shard-1	75.58% <100.00%> (+17.24%)	⬆️
shard-2	84.10% <100.00%> (+31.98%)	⬆️
shard-3	96.51% <100.00%> (+46.49%)	⬆️

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	99.61% <100.00%> (+<0.01%)	⬆️

... and 644 files with indirect coverage changes