fix(subsync): sync subtitles from stream URLs, auto-discover tool paths

- Download URL-loaded subtitle tracks (Aniyomi extension streams, Jellyfin) to a temp file first, reusing mpv's own request headers, instead of rejecting them with "Subtitle file not found"
- Pass mpv's headers through to ffmpeg for internal track extraction from streams too
- Auto-discover alass/ffsubsync/ffmpeg on PATH and common install prefixes when the config path is empty, instead of a hard-coded /usr/bin fallback that never exists on macOS
- Log subsync failures to the app log, not just a toast that vanishes in seconds
- Update docs-site and README credits for the new behavior

CHANGELOG.md

@@ -12,6 +12,9 @@
 
 ### Fixed
 
+- Subtitle Sync On Streams: Subsync now works when mpv loaded a subtitle track from a URL, which is how Aniyomi extension streams and Jellyfin add theirs. Such a track is downloaded to a temporary file first — reusing mpv's own request headers, so authenticated and referer-gated hosts stay reachable — instead of being rejected with "Subtitle file not found: https://…". This applies to both the sync target and the alass reference, so a Jimaku or TsukiHime download can now be retimed against a stream's own subtitles. Internal tracks of a stream also pass mpv's headers through to `ffmpeg`.
+- Subsync Tool Discovery: Leaving `subsync.alass_path`, `ffsubsync_path`, or `ffmpeg_path` empty now actually auto-discovers the binary, as the config help has always claimed. Previously it fell back to a hard-coded `/usr/bin/<tool>`, which does not exist on macOS and broke subsync for every default-config install there. Discovery searches `PATH` plus the usual install prefixes (a GUI launch inherits a minimal `PATH`) and accepts `alass-cli` as well as `alass`. An explicitly configured path is still used verbatim and never silently substituted.
+- Subsync Logging: Subsync failures are now written to the application log. Previously the only trace was an OSD toast that vanished after a few seconds, leaving nothing to diagnose from.
 - Anime Browser Window Switching: Opening the anime browser now shows a tray icon on every platform and — on macOS — puts the app in the Cmd+Tab switcher (which requires the Dock icon; the two are inseparable on macOS), so you can switch between it and mpv. Previously the subtitle overlay's fullscreen support hid the whole app from the Dock and Cmd+Tab, leaving no way to reach the window. The Dock icon is released again when the window closes during playback.
 - Anime Browser Playback Session: Launching a video from the anime browser now starts a regular SubMiner session (tray icon plus the on-demand overlay runtime), and in `subminer anime` standalone mode, closing the browser window during playback no longer quits the app and kills the stream — the window can be reopened from the tray while mpv keeps playing.