feat: self-managing yt-dlp + ffmpeg version display

yt-dlp is now a managed, auto-updating binary rather than a static bundled
one. On launch AeroFetch seeds a writable copy under userData from the
bundled seed, self-heals it if it goes missing, and — throttled to once a
day — self-updates it to the configured channel (default: nightly). This
keeps the binary current so YouTube changes don't silently cause 403s, and
an app reinstall (or portable re-extraction) can no longer roll it back.
Settings shows an auto-update toggle, the live version, last-checked time,
and the channel selector.

Also surface the bundled ffmpeg/ffprobe versions in Settings (display only:
they have no self-update path and, unlike yt-dlp, don't break as sites
change, so there is no auto-update for them).

- binaries: split the read-only bundled seed from the managed userData copy
- ytdlp: ensureManagedYtdlp (seed + self-heal), startup auto-update runner
- ytdlpPolicy: pure once-a-day throttle decision (unit-tested)
- ffmpeg: parse ffmpeg/ffprobe -version for the Settings panel
- settings/ipc/preload/renderer: new settings, IPC channels, types, and UI

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

src/main/index.ts

@@ -10,7 +10,8 @@ import {
   type YtdlpUpdateChannel,
   type SystemThemeInfo
 } from '@shared/ipc'
-import { getYtdlpVersion, updateYtdlp } from './ytdlp'
+import { getYtdlpVersion, updateYtdlp, runStartupYtdlpAutoUpdate } from './ytdlp'
+import { getFfmpegVersions } from './ffmpeg'
 import { checkForAppUpdate, downloadAppUpdate, runAppUpdate } from './updater'
 import { probeMedia } from './probe'
 import { startDownload, cancelDownload, previewCommand } from './download'
@@ -190,6 +191,8 @@ function registerIpcHandlers(): void {
 
   ipcMain.handle(IpcChannels.ytdlpVersion, () => getYtdlpVersion())
 
+  ipcMain.handle(IpcChannels.ffmpegVersion, () => getFfmpegVersions())
+
   ipcMain.handle(IpcChannels.probe, (_e, url: string) => probeMedia(url))
 
   ipcMain.handle(IpcChannels.downloadStart, (e, opts: StartDownloadOptions) => {
@@ -353,6 +356,16 @@ if (isPrimaryInstance) {
     registerSendToShortcut()
     createWindow()
 
+    // Keep yt-dlp current on its own: seed the managed copy, then (throttled to
+    // once a day) self-update it to the chosen channel so a stale binary can't
+    // silently cause YouTube 403s. Best-effort and off the critical path — it
+    // never blocks startup, and status is pushed to the window if it's listening.
+    runStartupYtdlpAutoUpdate((status) => {
+      if (mainWindow && !mainWindow.isDestroyed()) {
+        mainWindow.webContents.send(IpcChannels.ytdlpAutoUpdateStatus, status)
+      }
+    }).catch(() => {})
+
     app.on('activate', () => {
       if (BrowserWindow.getAllWindows().length === 0) createWindow()
     })