fix(jellyfin): find mpv when SubMiner is launched from Finder (#298)

changes/macos-mpv-discovery-docs.md

@@ -0,0 +1,4 @@
+type: docs
+area: docs
+
+- Documented how casting finds mpv on every platform, added a troubleshooting entry for casts that never start mpv, and noted that macOS 27 renames the Accessibility privacy list to "Device Control and Data Access".

changes/macos-mpv-discovery.md

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+type: fixed
+area: jellyfin
+
+- Fixed casting from Jellyfin on macOS when SubMiner is opened from Finder, the Dock, or Spotlight. SubMiner now honors `mpv.executablePath` and `SUBMINER_MPV_PATH` on macOS and Linux, and on macOS also finds mpv in `/opt/homebrew/bin`, `/usr/local/bin`, and `/Applications/mpv.app` instead of failing with `connect ENOENT /tmp/subminer-socket`.
+- The subtitle timing preview uses the same mpv lookup.