Implement manifest watcher

[2witstudios]

Epic 4: WebSocket & Real-Time Push — Issue 2/3

Source: 2-agent watcher pattern

Description

Dual-source manifest change detection that broadcasts updates to connected WebSocket clients.

Acceptance Criteria

• fs.watch on manifest.json with 300ms debounce
• Status polling at 3s interval (calls checkAgentStatus() for live status)
• Tracks previous agent statuses — sends individual agent:status events on change
• Broadcasts full manifest:updated event on manifest file change
• Graceful error handling for in-flight writes (manifest may be partially written)
• Cleanup on server shutdown
• Tests: debounce, status change detection, broadcast

Dependencies

• Requires: Implement WebSocket handler and event system #73 (WebSocket handler)

Files to Create/Modify

• src/server/ws/watcher.ts (new)
• src/server/ws/watcher.test.ts (new)