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/binaries.ts

@@ -13,10 +13,31 @@ export function getBinDir(): string {
   return is.dev ? join(app.getAppPath(), 'resources', 'bin') : join(process.resourcesPath, 'bin')
 }
 
-export function getYtdlpPath(): string {
+/**
+ * AeroFetch keeps its OWN writable copy of yt-dlp.exe under userData, separate
+ * from the read-only bundled seed in resources/bin. The managed copy is what
+ * actually gets spawned and self-updated (`--update-to`), so an app reinstall or
+ * portable re-extraction — which only ever replace the bundled seed — can never
+ * roll a freshly-updated yt-dlp back to a stale version. See ensureManagedYtdlp
+ * in ytdlp.ts, which seeds this from getBundledYtdlpPath() on first run.
+ *
+ * ffmpeg/ffprobe/aria2c stay in getBinDir(): they're not self-updating and
+ * yt-dlp finds them via `--ffmpeg-location <binDir>`.
+ */
+export function getManagedBinDir(): string {
+  return join(app.getPath('userData'), 'bin')
+}
+
+/** The bundled, read-only yt-dlp.exe seeded into the managed copy when missing. */
+export function getBundledYtdlpPath(): string {
   return join(getBinDir(), 'yt-dlp.exe')
 }
 
+/** The managed (spawned + auto-updated) yt-dlp.exe under userData. */
+export function getYtdlpPath(): string {
+  return join(getManagedBinDir(), 'yt-dlp.exe')
+}
+
 export function getFfmpegPath(): string {
   return join(getBinDir(), 'ffmpeg.exe')
 }