fix(review): meter issue planner AI usage

[JSONbored]

Motivation

• Prevent unmetered Workers-AI spend from the @gittensory plan command by enforcing the repo/global AI budget and avoiding bursty actor-driven consumption.
• Ensure planner actions are recorded in the shared AI usage accounting so the existing daily neuron budget gating works across features.
• Reduce risk of cross-tenant resource exhaustion by adding a short per-actor/per-repo cooldown to avoid repeated planner-trigger spam.

Description

• Enforce budget and record usage in the planner by adding neuron estimation and pre-checks in generateIssuePlan using estimateNeurons, sumAiEstimatedNeuronsSince, and a new recordPlannerUsage wrapper that writes ai_usage_events rows (statuses: ok, no_output, quota_exceeded).
• Add a per-actor/per-repo cooldown for @gittensory plan in maybeProcessPlanCommand with ISSUE_PLAN_COOLDOWN_MS and the helper isPlanCommandCoolingDown which checks recent audit_events to avoid repeated AI spend.
• Wire accounting/cooldown into src/review/planner.ts and src/queue/processors.ts, and update tests in test/unit/planner.test.ts and test/unit/queue.test.ts to cover budget and cooldown behavior.

Testing

• Ran npx vitest run test/unit/planner.test.ts and all planner unit tests passed (12/12).
• Ran targeted queue tests for the planner with npx vitest run test/unit/queue.test.ts -t "planner" and the planner-related queue tests passed (planner cases succeeded; unrelated long-running queue tests were skipped in the targeted run).
• Ran npm run typecheck (tsc --noEmit) and typechecking succeeded.
• Started npm run test:coverage (full coverage) but the coverage run did not complete within the interactive run window; targeted unit tests above demonstrate the new budget/cooldown behavior passed.

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Codex Task

[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 95.34%. Comparing base (6138b9e) to head (5541fc5).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1403   +/-   ##
=======================================
  Coverage   95.33%   95.34%           
=======================================
  Files         192      192           
  Lines       20750    20770   +20     
  Branches     7500     7507    +7     
=======================================
+ Hits        19783    19803   +20     
  Misses        383      383           
  Partials      584      584           

Files with missing lines	Coverage Δ
src/queue/processors.ts	87.68% <100.00%> (+0.07%)	⬆️
src/review/planner.ts	100.00% <100.00%> (ø)

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