Tracker observer loop: poll + ApplyTrackerFacts into LCM #35

Context

Tracker v1 is write-mostly (Get for spawn-bootstrap, Comment for session updates, Transition for state changes). Pull-on-demand from SM, no goroutine, no facts-into-LCM.

This issue tracks the v2 work: an observer loop that polls tracker state and pushes facts into LCM, mirroring adil's SCM observer pattern (PR #28) and our reaper pattern (PR #29).

Scope

• New goroutine per project that polls each tracker on a configurable cadence.
• New typed ApplyTrackerFacts(...) method on LifecycleManager.
• DECIDE consumes tracker facts (e.g., issue reassigned -> session-orphaned reaction; issue closed externally -> session-cancelled; new comment with bot mention -> nudge reaction).
• Per-project enable/disable config (some users won't want polling overhead).
• Rate-limit / backoff strategy for each provider.

Why deferred

• LCM doesn't currently consume tracker state; no reactions are defined.
• Polling cadence + rate-limit design needs its own design pass.
• Webhook alternative may be better for some providers (Linear has webhooks; GitHub does too) — needs the HTTP daemon (aditi's lane).

Related

• Mirrors SCM observer pattern from PR feat: integrate GitHub SCM flow #28 (adil).
• Mirrors reaper-goroutine pattern from PR feat(observe): reaper for liveness probe + TickEscalations heartbeat (#9) #29 (us).
• Depends on Tracker port landing first (Tracker interface in ports/outbound.go).