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/startup/stub.go

@@ -8,4 +8,10 @@ func Enable() error { return nil }
 
 func Disable() error { return nil }
 
+func WatchdogEnabled() bool { return false }
+
+func EnableWatchdog() error { return nil }
+
+func DisableWatchdog() error { return nil }
+
 func SyncInstalledPath() error { return nil }