fix(review): include violation count and ban proximity in moderation escalation comments

[JSONbored]

Summary

• A mod:warning/mod:banned label alone doesn't tell anyone reading the closure how many violations are on record or how close a contributor is to an automatic ban.
• applyModerationEscalationForRule now posts a follow-up comment stating the current violation count, the configured ban threshold, whether a blacklist entry was actually added (vs. auto-blacklist being disabled or a write failure), and the decay window when one is configured.
• New pure buildModerationEscalationComment helper, directly unit tested for every tier/blacklisted/decay combination.

Test plan

• npx vitest run test/unit/agent-action-executor.test.ts — 172/172 passing
• Coverage scoped to the diff: 100% of changed lines and branches covered (verified via lcov DA/BRDA against the diff hunks), including a real D1-write-failure test (vi.spyOn on env.DB.prepare) rather than an ignore annotation
• npm run test:coverage (full, unsharded) — all green, no regressions
• npx tsc --noEmit clean
• npm audit --audit-level=moderate clean

[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 88.50%. Comparing base (4d9b9d1) to head (7f17edd).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7640      +/-   ##
==========================================
- Coverage   88.51%   88.50%   -0.02%     
==========================================
  Files         724      724              
  Lines       75992    76004      +12     
  Branches    22618    22622       +4     
==========================================
+ Hits        67263    67264       +1     
- Misses       7681     7688       +7     
- Partials     1048     1052       +4     

Flag	Coverage Δ
shard-1	35.71% <0.00%> (-0.01%)	⬇️
shard-2	32.95% <0.00%> (-0.03%)	⬇️
shard-3	28.61% <100.00%> (-0.03%)	⬇️
shard-4	40.52% <35.71%> (-0.11%)	⬇️
shard-5	33.98% <0.00%> (-0.02%)	⬇️
shard-6	35.92% <0.00%> (-0.11%)	⬇️

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Files with missing lines	Coverage Δ
src/services/agent-action-executor.ts	97.13% <100.00%> (+0.11%)	⬆️

... and 2 files with indirect coverage changes