# Idle Detection for WindowWatcher

## Summary

Add idle detection to WindowWatcher so it automatically pauses the active TaskTracker task when the user is away, and resumes it when they return.

## Behavior

- **Detection method:** `GetLastInputInfo` Win32 API — returns time of last keyboard/mouse input
- **Idle threshold:** Configurable via `IdleTimeoutMs` (default: 300,000ms = 5 minutes)
- **Checked on existing poll cycle** — no new timers or threads

### State Machine

```
ACTIVE  ──(idle > threshold)──►  IDLE
  ▲                                │
  └──(input detected)──────────────┘
```

### On Idle Transition

1. `GET /api/tasks/active` to find the current task
2. `PUT /api/tasks/{id}/pause` with note "Auto-paused: idle timeout"
3. Store paused task ID locally

### On Resume Transition

1. Check if stored task ID is still in Paused status
2. If yes: `PUT /api/tasks/{id}/resume` with note "Auto-resumed: user returned"
3. Clear stored task ID

## Files Changed

| File | Change |
|------|--------|
| `NativeMethods.cs` | Add `GetLastInputInfo` + `LASTINPUTINFO` struct |
| `Worker.cs` | Add idle state tracking, check idle time each poll, call pause/resume APIs |
| `WindowWatcherOptions.cs` | Add `IdleTimeoutMs` (default: 300000) |
| `appsettings.json` | Add `IdleTimeoutMs` setting |

## Edge Cases

- **No active task when idle fires:** Log, skip pause, don't store task ID
- **Task manually changed while idle:** On resume, verify stored task is still paused before resuming
- **API unreachable:** Log warning, retry on next poll cycle. Maintain idle state locally

## Out of Scope

- Session lock/unlock detection
- New context event types
- Tray menu UI changes