feat: implement work heartbeat service for health checks and task dispatching

- Introduced a new heartbeat service that runs at defined intervals to perform health checks on workers and fill available task slots based on priority.
- Added a health tool to scan worker health across projects with optional auto-fix capabilities.
- Updated the status tool to provide a lightweight overview of worker states and queue counts without health checks.
- Enhanced task creation tool descriptions to clarify task state handling.
- Implemented tests for the work heartbeat logic, ensuring proper project resolution, worker state management, and task prioritization.

lib/dispatch.ts

@@ -1,5 +1,5 @@
 /**
- * dispatch.ts — Core dispatch logic shared by work_start, auto_pickup, and projectTick.
+ * dispatch.ts — Core dispatch logic shared by work_start, work_heartbeat, and projectTick.
  *
  * Handles: session lookup, spawn/reuse via Gateway RPC, task dispatch via CLI,
  * state update (activateWorker), and audit logging.