feat(pulse): remove pendingTasksWatcher polling workaround (Phase 3)

Phase 1 added buildPendingTasksFromEvents (correct event-fold approach).
Phase 2 wired it into rebuildSnapshot/runPulse.
Phase 3 removes the old polling workaround (pending-tasks.ts).

The polling workaround (pending-tasks.ts) was only on feat/task-dispatch-loop
and never merged to main. This commit cleans up the last reference to
pendingTasksWatcher in pending-tasks-projection.ts comments.

Ref #83

Made-with: Cursor

Co-authored-by: 小橘 <xiaoju@shazhou.work>

packages/pulse/src/watchers/pending-tasks-projection.ts

@@ -7,9 +7,7 @@ import type {
 
 /**
  * Fold all task-* events from the store into the current pending-tasks state.
- *
- * Replaces the old pendingTasksWatcher (polling workaround).
- * Should be called during each rebuildSnapshot cycle.
+ * Called during each rebuildSnapshot cycle.
  */
 export function buildPendingTasksFromEvents(
   store: PulseStore,