fix(review): correct the per-project fairness-flags tile's row-count label

[JSONbored]

Summary

• The operator dashboard's "Contributor fairness flags" tile delta said "N contributor(s) evaluated", but contributorGateEval.rows is one row per (login, project) -- a login active on two repos contributes two rows, so the old wording overstated the number of distinct contributors.
• Reworded to "N (login, project) row(s) evaluated". The newer "Global contributor fairness flags" tile (added in feat(review): add a global cross-repo blended contributor trust score #7711) already has an accurate per-login count, since it folds by login alone.

Test plan

• npx tsc --noEmit clean
• operator-dashboard.test.ts + api.test.ts green
• 100% line/branch coverage on operator-dashboard.ts (verified via lcov)

[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 88.59%. Comparing base (a964eaf) to head (f996de4).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7716       +/-   ##
===========================================
+ Coverage   62.31%   88.59%   +26.27%     
===========================================
  Files         725       84      -641     
  Lines       76397    20704    -55693     
  Branches    22758     3660    -19098     
===========================================
- Hits        47608    18342    -29266     
+ Misses      25083     2184    -22899     
+ Partials     3706      178     -3528     

Flag	Coverage Δ
shard-1	85.00% <100.00%> (?)
shard-2	7.50% <0.00%> (-45.09%)	⬇️
shard-3	77.50% <0.00%> (?)

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

Files with missing lines	Coverage Δ
src/services/operator-dashboard.ts	100.00% <100.00%> (+15.00%)	⬆️

... and 641 files with indirect coverage changes