watch --count and --timeout

[0xLeif]

Part of GOAL.md workstream B.

aps watch runs forever today; agents need bounded execution. Add --count N (stop after N emitted values) and --timeout SECONDS (stop after wall-clock budget). Both optional, composable, and orthogonal to the existing shouldContinue seam in StateStore.watchBlocking.

Acceptance criteria

• --count 1 prints the current value once and exits 0 (useful as a JSONL-friendly get)
• --timeout expires cleanly with exit 0 and no partial line
• Bounds are covered by unit tests (no multi-second sleeps; small poll intervals)
• specs/state-store/state-store.spec.md updated in the same change

[0xLeif]

Shipped in PR #2 (aps 0.2.0, merge commit 62198af). Verified in review: gates green, behavior confirmed locally.