Fix L29/L52: QUALITY_OPTIONS moved to UI module; installer spawn via child_process

L29: QUALITY_OPTIONS was a presentational constant living in store/downloads.ts,
     coupling views to the store. Moved to src/renderer/src/qualityOptions.ts,
     which assembles it directly from @shared/ipc. store/downloads.ts no longer
     imports VIDEO/AUDIO_QUALITY_OPTIONS. Both consumers (DownloadBar, SettingsView)
     updated to import from the new module.

L52: Replaced the fixed `setTimeout(app.quit, 1500)` installer handoff with a
     detached spawn. The installer is spawned with stdio:'ignore' and unref'd so
     it outlives AeroFetch even on a slow machine. app.quit() fires on setImmediate
     so the IPC response returns to the renderer before the process exits.

typecheck + 242 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/updater.ts

@@ -1,4 +1,5 @@
-import { app, net, shell, type WebContents } from 'electron'
+import { app, net, type WebContents } from 'electron'
+import { spawn } from 'child_process'
 import { createWriteStream, type WriteStream } from 'fs'
 import { stat, unlink } from 'fs/promises'
 import { join, normalize, dirname } from 'path'
@@ -413,9 +414,6 @@ export async function downloadAppUpdate(url: string, wc: WebContents): Promise<A
   })
 }
 
-/** Let the launched installer spawn before we quit to release our files (ms). */
-const INSTALLER_HANDOFF_MS = 1500
-
 /** Launch a freshly-downloaded installer, then quit so it can replace the app. */
 export async function runAppUpdate(filePath: string): Promise<{ ok: boolean; error?: string }> {
   try {
@@ -428,10 +426,13 @@ export async function runAppUpdate(filePath: string): Promise<{ ok: boolean; err
       return { ok: false, error: 'Refused to run an unexpected file.' }
     }
     await stat(target) // throws if the file is missing
-    const err = await shell.openPath(target) // hand the installer to the OS
-    if (err) return { ok: false, error: err }
-    // Give the installer a beat to spawn, then quit so it can overwrite our files.
-    setTimeout(() => app.quit(), INSTALLER_HANDOFF_MS)
+    // Spawn the installer detached + unref'd so it outlives our process even on a
+    // slow machine. shell.openPath goes through ShellExecute but gives us no child
+    // PID to wait on; spawning directly lets us call unref() before we quit.
+    const child = spawn(target, [], { detached: true, stdio: 'ignore', shell: false })
+    child.unref()
+    // Let the IPC response reach the renderer before we exit.
+    setImmediate(() => app.quit())
     return { ok: true }
   } catch (e) {
     return { ok: false, error: e instanceof Error ? e.message : String(e) }