feat(sync-ui): defer app quit until async cleanup resolves

- check-host participates in active-run coordination and can be cancelled
- shutdown() cancels and awaits the active launcher run on quit
- onWillQuit calls preventDefault and re-triggers quit once cleanup settles
- Snapshot mode awaits tracker quiescent before writing output
- Auto-scheduler catches synchronous triggerHostSync failures
- SCP endpoint accepts Windows absolute paths; cmd.exe rejects % in quoted values
- runAppCommand unified (inherit vs pipe stdio) in launcher/mpv.ts
- Docs: add --check, --json, --ui, --sync-cli, --make-temp/--remove-temp examples

src/core/services/stats-sync/ssh.ts

@@ -35,6 +35,7 @@ export function runSsh(host: string, remoteCommand: string): RemoteRunResult {
 }
 
 function assertSafeScpEndpoint(endpoint: string): void {
+  if (/^[A-Za-z]:[\\/]/.test(endpoint)) return;
   const colon = endpoint.indexOf(':');
   const slash = endpoint.indexOf('/');
   if (colon <= 0 || (slash !== -1 && slash < colon)) {
@@ -116,6 +117,9 @@ export function quoteForRemoteShell(flavor: RemoteShellFlavor, value: string): s
   if (value.includes('"')) {
     throw new Error(`Refusing to quote a value with quotes for a Windows shell: ${value}`);
   }
+  if (value.includes('%')) {
+    throw new Error(`Refusing to quote a value with percent signs for cmd.exe: ${value}`);
+  }
   return `"${value}"`;
 }