feat(player): C hotkey toggles the lyrics overlay

YT parity. "C" clicks the visible #ytpLyricsBtn when there is one (music
type), no-op otherwise so hitting C next to K / L / M on a plain video
doesn't trigger something unexpected.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

resources/views/components/video-player.blade.php

@@ -1505,6 +1505,16 @@ document.addEventListener('keydown', e => {
             e.preventDefault(); theaterBtn && theaterBtn.click(); break;
         case 'i': case 'I':
             e.preventDefault(); pipBtn && !pipBtn.classList.contains('unsupported') && pipBtn.click(); break;
+        case 'c': case 'C':
+            // Captions / lyrics toggle — click the lyrics button when the
+            // page has one (music type). On a video that has no lyrics
+            // the key is a no-op; we don't throw up a toast because the
+            // viewer may just be hitting letters next to K / L / M.
+            {
+                const lyr = document.getElementById('ytpLyricsBtn');
+                if (lyr && lyr.offsetParent !== null) { e.preventDefault(); lyr.click(); showControls(); }
+            }
+            break;
         case 'j': case 'J':
             e.preventDefault(); seekRelative(-10); flashDbl(dblLeft); showControls(); break;
         case 'l': case 'L':