chore(fullscreen-player): drop dead i18n keys and old CSS (#1002)

Follow-up cleanup after the old fullscreen player was removed (#1001):
- remove the 9 now-unused settings i18n keys (fsPlayerSection,
  fsShowArtistPortrait(+Desc), fsPortraitDim, fsLyricsStyle(+Rail/Apple
  +Descs)) across all 9 locales.
- reduce fullscreen-player-adaptive-portrait.css to the shared lyrics
  overlay styles (FsLyricsApple); drop the old player's .fs-*, the
  .fslm-* lyrics menu, the unused .fsa-fade-* and dead keyframes.

src/locales/en/settings.ts

@@ -588,20 +588,11 @@ export const settings = {
   infiniteQueue: 'Infinite Queue',
   infiniteQueueDesc: 'Automatically append random tracks when the queue runs out',
   experimental: 'Experimental',
-  fsPlayerSection: 'Fullscreen Player',
-  fsLyricsStyle: 'Lyrics style',
-  fsLyricsStyleRail: 'Rail',
-  fsLyricsStyleRailDesc: 'Classic 5-line sliding rail.',
-  fsLyricsStyleApple: 'Scrolling',
-  fsLyricsStyleAppleDesc: 'Full-screen scrollable list.',
   sidebarLyricsStyle: 'Lyrics scroll style',
   sidebarLyricsStyleClassic: 'Classic',
   sidebarLyricsStyleClassicDesc: 'Scroll active line to center.',
   sidebarLyricsStyleApple: 'Apple Music-like',
   sidebarLyricsStyleAppleDesc: 'Active line anchors near the top with smooth spring transitions.',
-  fsShowArtistPortrait: 'Show artist photo',
-  fsShowArtistPortraitDesc: 'Display the artist photo (or album art) on the right side of the fullscreen player.',
-  fsPortraitDim: 'Photo dimming',
   seekbarStyle: 'Seekbar Style',
   seekbarStyleDesc: 'Choose the look of the player seek bar',
   seekbarTruewave: 'Truewave',