fix(sync): harden detached launch, bounded --check probes, and pipe-clos

- `sync --ui` now launches detached; closing standalone Sync window exits app
- `--check` uses BatchMode + ConnectTimeout + 15s timeoutMs on all SSH calls
- `runSyncLauncher` settles on `exit` (not just `close`) for Electron pipe inheritance
- Added `timeoutMs` to `runSyncLauncher`; check-host passes 30s deadline
- `handleSyncCliAtEntry` wraps exit deps for testability; fixes Linux AppImage GUI fallthrough
- `config-settings-window` gains optional `onClosed` hook
- Added preload-syncui bundle to `build:syncui` script

launcher/commands/app-command.ts

@@ -1,14 +1,17 @@
 import {
+  launchAppCommandDetached,
   launchAppBackgroundDetached,
   launchTexthookerOnly,
-  runAppCommandInteractive,
   runAppCommandWithInherit,
 } from '../mpv.js';
 import type { LauncherCommandContext } from './context.js';
 
 type AppCommandDeps = {
   runAppCommandWithInherit: (appPath: string, appArgs: string[]) => void;
-  runAppCommandInteractive: (appPath: string, appArgs: string[]) => void;
+  launchSyncUiDetached: (
+    appPath: string,
+    logLevel: LauncherCommandContext['args']['logLevel'],
+  ) => void;
   launchAppBackgroundDetached: (
     appPath: string,
     logLevel: LauncherCommandContext['args']['logLevel'],
@@ -17,7 +20,8 @@ type AppCommandDeps = {
 
 const defaultAppCommandDeps: AppCommandDeps = {
   runAppCommandWithInherit,
-  runAppCommandInteractive,
+  launchSyncUiDetached: (appPath, logLevel) =>
+    launchAppCommandDetached(appPath, ['--sync-window'], logLevel, 'sync-ui'),
   launchAppBackgroundDetached,
 };
 
@@ -34,7 +38,7 @@ export function runAppPassthroughCommand(
     return true;
   }
   if (args.syncUi) {
-    deps.runAppCommandInteractive(appPath, ['--sync-window']);
+    deps.launchSyncUiDetached(appPath, args.logLevel);
     return true;
   }
   if (!args.appPassthrough) {