P2-A: Idle Scheduler (UNBLOCKS: Daydreamer operations)

[github-actions]

Why: Need cooperative background loop that doesn't block foreground.

• P2-A1: Implement daydreamer/IdleScheduler.ts

  • Loop via requestIdleCallback (browser) or setImmediate (Node)
  • Interruptible (yield after N ms of work)
  • CPU budget awareness (pause if main thread busy)
  • Task queue (prioritize high-value work)

• P2-A2: Add scheduler test coverage

  • tests/daydreamer/IdleScheduler.test.ts
  • Test cooperative yielding
  • Test interruption doesn't corrupt state

Exit Criteria: Background loop runs without blocking UI.