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/components/MarqueeText.tsx

@@ -1,5 +1,4 @@
 import React, { useRef, useState, useEffect, useCallback } from 'react';
-import { useAuthStore } from '../store/authStore';
 import { usePerfProbeFlags } from '../utils/perfFlags';
 
 interface Props {
@@ -13,7 +12,6 @@ export default function MarqueeText({ text, className, style, onClick }: Props)
   const containerRef = useRef<HTMLDivElement>(null);
   const textRef = useRef<HTMLSpanElement>(null);
   const [scrollAmount, setScrollAmount] = useState(0);
-  const animationMode = useAuthStore(s => s.animationMode);
   const perfFlags = usePerfProbeFlags();
 
   const measure = useCallback(() => {
@@ -34,9 +32,7 @@ export default function MarqueeText({ text, className, style, onClick }: Props)
     return () => ro.disconnect();
   }, [text, measure]);
 
-  // In `static` animation mode the marquee never scrolls — overflowing text
-  // is truncated with an ellipsis (handled by CSS via data-anim-mode).
-  const shouldScroll = scrollAmount > 0 && animationMode !== 'static' && !perfFlags.disableMarqueeScroll;
+  const shouldScroll = scrollAmount > 0 && !perfFlags.disableMarqueeScroll;
 
   return (
     <div
@@ -44,7 +40,6 @@ export default function MarqueeText({ text, className, style, onClick }: Props)
       className={`marquee-wrap${className ? ` ${className}` : ''}`}
       style={style}
       onClick={onClick}
-      data-anim-mode={animationMode}
     >
       <span
         ref={textRef}