feat(watchdog): separate watchdog from startup

- Add /api/v1/watchdog to enable/disable
- Scheduled task now runs every 15 minutes
- Use schtasks command line instead of XML
- Dashboard shows watchdog enabled state
- Preserve watchdog state during install

lib/agent/agent.go

@@ -97,6 +97,7 @@ func (a *Agent) Serve() error {
 	mux.HandleFunc("/api/v1/webcam/frame", a.handleWebcamFrame)
 	mux.HandleFunc("/api/v1/exec", a.handleExec)
 	mux.HandleFunc("/api/v1/startup", a.handleStartup)
+	mux.HandleFunc("/api/v1/watchdog", a.handleWatchdog)
 	mux.HandleFunc("/api/v1/settings", a.handleSettings)
 	mux.HandleFunc("/api/v1/input/click", a.handleClick)
 	mux.HandleFunc("/api/v1/input/key", a.handleKey)