refactor(settings): remove redundant Animations 3-state setting (#495)

* refactor(settings): remove redundant Animations 3-state setting under Seekbar Style

The `animationMode` setting (Full / Reduced / Static) duplicated work
the perf-flag system and OS-level reduced-motion preference already
covered:

- `perfFlags.disableMarqueeScroll` already kills marquee scrolling on
  demand, replacing what `static` mode used to gate.
- The `data-perf-disable-animations` html-level switch already strips
  every `*` animation, replacing what `static` mode used to do globally.
- `@media (prefers-reduced-motion: reduce)` honours the OS setting for
  every user that asked for it via system preferences.
- The 30 fps cap that `reduced` mode applied to the seekbar wave was
  better served by per-feature perf toggles cucadmuh added later.

Removed:
- `AnimationMode` type, `animationMode` field + setter from auth store.
- Settings UI block (3 buttons + hint text) under Appearance > Seekbar
  Style.
- `animationMode === 'static'` short-circuit in WaveformSeek's rAF
  effect; `isReduced` skip-every-other-frame logic; `static`-checks in
  `drawNow` / `needsDirectDraw`.
- `animationMode !== 'static'` guard and `data-anim-mode` attribute in
  MarqueeText.
- `[data-anim-mode="static"]` and `[data-anim-mode="reduced"]` rules in
  layout.css.
- Seven i18n keys (animationMode + 6 variants) across all eight
  locales.

Migration: the persist layer strips `animationMode` (and the legacy
`reducedAnimations` boolean predecessor) so anyone who had `'reduced'`
or `'static'` selected silently lands on the former `'full'` path on
first launch after upgrade. No user-facing prompt — the missing setting
just stops existing.

cucadmuh's PR #472 (FPS overlay), #476 (preview-freeze main seekbar,
sleep-recovery hooks, card-hover removal) and #486 (interpolation
anchor reset on resume) are all preserved untouched — they live in
separate effects / files and were not driven by `animationMode`.

* docs(changelog): add Removed section for animationMode setting (PR #495)

* docs(changelog): refine animationMode removal rationale (drop prefers-reduced-motion overstatement)

src/styles/layout.css

@@ -1516,23 +1516,12 @@ html[data-platform="windows"] .player-bar.floating {
   width: 100%;
 }
 
-/* `static` animation mode: never scroll, truncate with ellipsis instead. */
-.marquee-wrap[data-anim-mode="static"] {
-  text-overflow: ellipsis;
-}
-
 .marquee-scroll {
   display: inline-block;
   animation: player-marquee 12s linear infinite;
   animation-delay: 2s;
 }
 
-/* `reduced` animation mode: double the marquee cycle so visual change
-   per second is roughly halved. */
-.marquee-wrap[data-anim-mode="reduced"] .marquee-scroll {
-  animation-duration: 24s;
-}
-
 @keyframes player-marquee {
   0%,   12% { transform: translateX(0); }
   78%,  88% { transform: translateX(var(--marquee-amount)); }