per-track language override on audio detail page

adds stream_decisions.custom_language (ISO 639-2 code or null) so the
user can correct a mislabeled audio track — e.g. a Spanish dub tagged
"und" in the container — without going through Jellyfin. the override
wins over stream.language everywhere it matters: the analyzer reads it
for keep/remove decisions and track ordering, the ffmpeg command builder
writes it as both the language metadata tag and the harmonized track
title, and reanalyze preserves it across reruns and rescans.

on the audio detail page, each pending audio row swaps its language
cell for an inline <select> populated from LANG_NAMES. picking the raw
file language clears the override; anything else sets it and triggers a
server-side reanalyze so keep/remove + target_index update immediately.
a small ✎ hint marks overridden tracks. rebuilt commands tag the output
accordingly so Jellyfin reads the corrected language.

PATCH /api/review/:id/stream/:streamId/language validates the code
against LANG_NAMES (accepts ISO 639-1/2/2B aliases, rejects garbage)
and runs reanalyze inside.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/types.ts

@@ -76,6 +76,11 @@ export interface StreamDecision {
 	action: "keep" | "remove";
 	target_index: number | null;
 	custom_title: string | null;
+	/** Per-stream language override. When set, the analyzer and ffmpeg
+	 * command builder both read this in preference to the raw
+	 * media_streams.language. Lets the user correct an "und" or
+	 * mislabeled audio track without going through Jellyfin. */
+	custom_language: string | null;
 	transcode_codec: string | null;
 }