Backlog: Wire adapter notifier lifecycle into executor runner

[alekspetrov]

Problem

All 9 adapters implement NotifyTaskStarted, NotifyTaskCompleted, NotifyTaskFailed methods in their notifier.go files, but the executor runner never calls them. Task status updates don't propagate back to source systems (Linear, Jira, Asana, etc.).

Additionally, the Plane adapter has no notifier.go at all — it's the only adapter missing this file.

Scope

This is an architectural task requiring:

1. A dispatch mechanism in the runner to call the correct adapter's notifier based on issue source
2. Notifier interface standardization across all adapters
3. Creating internal/adapters/plane/notifier.go
4. Testing the full lifecycle for each adapter

Decision Needed

How should the runner dispatch to notifiers?

• Option A: Notifier interface on the issue/task struct, set during pickup
• Option B: Central notifier registry keyed by adapter name
• Option C: Callback functions passed through PollerOption/WebhookHandler

Not for immediate Pilot execution — requires design discussion first.