Fix subtitle positioning and show existing langs without re-downloading

- Strip yt-dlp's align:start position:0% cue settings from VTT files
  after both video download and subtitle-only download so CSS ::cue centers them
- CC chip now shows already-downloaded langs (e.g. 'CC: en') directly
  from disk with a '+' button to add more — no YouTube call needed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Watch.jsx

@@ -995,15 +995,18 @@ export default function Watch() {
               )}
 
               {(() => {
-                // Subs already on disk → show indicator (player CC button handles the rest)
+                // Subs already on disk → show langs + "+" to add more
                 if (subtitleFiles.length > 0 && !subsRequested) return (
-                  <button
-                    onClick={() => setSubsRequested(true)}
-                    className="flex items-center gap-1 px-3 py-1.5 rounded-full bg-zinc-800 text-zinc-400 text-xs hover:bg-zinc-700 transition-colors"
-                    title="Subtitles loaded — click to add more languages"
-                  >
-                    CC ✓
-                  </button>
+                  <div className="flex items-center gap-1">
+                    <span className="px-3 py-1.5 rounded-full bg-zinc-800 text-zinc-400 text-xs font-mono">
+                      CC: {subtitleFiles.map(s => s.lang).join(", ")}
+                    </span>
+                    <button
+                      onClick={() => setSubsRequested(true)}
+                      className="px-2.5 py-1.5 rounded-full text-xs bg-zinc-800 text-zinc-500 hover:bg-zinc-700 transition-colors"
+                      title="Add subtitle language"
+                    >+</button>
+                  </div>
                 );
                 // Not yet asked → show CC chip
                 if (!subsRequested) return (