fix: prevent overlapping PR feedback runs

[danii1]

Summary

• make a healthy relay the primary source for PR review feedback and mentions
• retain 30-minute safety sweeps and automatically resume normal polling after relay silence
• keep PR lifecycle and conflict reconciliation on the configured polling cadence
• serialize relay, review-poll, and mention-poll handling per PR, collapsing overlap into one post-run reconciliation

Incident

PR #119 received the same feedback through relay, review polling, and mention polling before the first run persisted its addressed marker. Four agent runs overlapped for one effective request. Source-scoped event IDs prevented redelivery within each source but did not coordinate across sources.

Verification

• pre-commit: format, lint, typecheck
• pre-push: all monorepo tests and typecheck
• @getdevintern/code: 1,293 tests passed
• focused regression suites: 87 tests passed
• package build passed

Behavior

When relay long-polls are healthy, review and mention acquisition yield to relay. A safety sweep still runs every 30 minutes. If no successful relay poll is observed for at least 90 seconds or two configured poll intervals, whichever is longer, normal feedback polling resumes. Multiple acquisition events for the same PR share one active run and request at most one follow-up fetch after it completes.