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/shared/ipc.ts

@@ -15,6 +15,7 @@ export const IpcChannels = {
   /** main → renderer push channel for installer download progress */
   appUpdateProgress: 'app:update-progress',
   ytdlpVersion: 'ytdlp:version',
+  ffmpegVersion: 'ffmpeg:version',
   probe: 'media:probe',
   downloadStart: 'download:start',
   downloadCancel: 'download:cancel',
@@ -40,6 +41,8 @@ export const IpcChannels = {
   templatesRemove: 'templates:remove',
   commandPreview: 'command:preview',
   ytdlpUpdate: 'ytdlp:update',
+  /** main → renderer push channel for background yt-dlp auto-update status */
+  ytdlpAutoUpdateStatus: 'ytdlp:auto-update-status',
   errorLogList: 'errorlog:list',
   errorLogClear: 'errorlog:clear',
   backupExport: 'backup:export',
@@ -196,6 +199,18 @@ export interface YtdlpVersionResult {
   error?: string
 }
 
+/**
+ * Versions of the bundled ffmpeg + ffprobe, for display in Settings. Each is the
+ * parsed version token, or null when that binary is missing or unreadable. These
+ * ship with AeroFetch and aren't auto-updated (ffmpeg has no self-update and,
+ * unlike yt-dlp, doesn't break as sites change), so there's no ok/error here —
+ * just "what's installed".
+ */
+export interface FfmpegVersionResult {
+  ffmpeg: string | null
+  ffprobe: string | null
+}
+
 /** Result of checking the configured Gitea repo for a newer AeroFetch release. */
 export interface AppUpdateInfo {
   ok: boolean
@@ -260,6 +275,24 @@ export interface YtdlpUpdateResult {
   error?: string
 }
 
+/**
+ * Status of a background (startup) yt-dlp auto-update, pushed main → renderer on
+ * IpcChannels.ytdlpAutoUpdateStatus so the Settings UI can reflect a check that
+ * ran on its own — no button click needed.
+ */
+export interface YtdlpAutoUpdateStatus {
+  /** 'checking' when the update starts; the rest are terminal */
+  phase: 'checking' | 'updated' | 'current' | 'error'
+  /** which channel was checked */
+  channel: YtdlpUpdateChannel
+  /** yt-dlp version after the run, when known (phases 'updated' | 'current') */
+  version?: string
+  /** epoch ms the check finished (terminal phases) — feeds the "last checked" line */
+  checkedAt?: number
+  /** error text when phase === 'error' */
+  error?: string
+}
+
 /** A single selectable output format, derived from `yt-dlp -J`. */
 export interface FormatOption {
   /** yt-dlp format_id, or BEST_FORMAT_ID for the auto-best option */
@@ -437,6 +470,12 @@ export interface Settings {
   restrictFilenames: boolean
   /** record completed downloads in a yt-dlp --download-archive file to skip repeats */
   downloadArchive: boolean
+  /** keep the managed yt-dlp.exe auto-updated in the background on launch */
+  autoUpdateYtdlp: boolean
+  /** channel the auto-updater (and the manual "Update yt-dlp" button) updates to */
+  ytdlpChannel: YtdlpUpdateChannel
+  /** epoch ms of the last automatic yt-dlp update check; 0 = never run */
+  ytdlpLastUpdateCheck: number
   /** apply a named custom-command template's extra args to every new download */
   customCommandEnabled: boolean
   /** id of the CommandTemplate applied when customCommandEnabled is on; null = none picked yet */