feat(waveform): real amplitude waveform via Symphonia + smooth crossfade

Add Rust command `compute_waveform` that downloads the audio file,
seek-samples 500 evenly-spaced frames with Symphonia (fast path) and
computes peak amplitudes. Percentile-based normalisation (p5→p95)
preserves visible dynamics even for heavily compressed music.

Frontend caches results per track (module-level Map), shows the
pseudo-random fallback immediately and crossfades to the real waveform
over 400 ms (ease-in-out) once the computation finishes.

Also: Settings input-tab reset buttons now use btn-danger styling.

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

src/components/PlayerBar.tsx

@@ -7,6 +7,7 @@ import {
 import { usePlayerStore } from '../store/playerStore';
 import { useAuthStore } from '../store/authStore';
 import { buildCoverArtUrl, coverArtCacheKey, star, unstar } from '../api/subsonic';
+import { resolvePlaybackUrl } from '../utils/resolvePlaybackUrl';
 import CachedImage from './CachedImage';
 import WaveformSeek from './WaveformSeek';
 import Equalizer from './Equalizer';
@@ -39,6 +40,7 @@ export default function PlayerBar() {
     starredOverrides, setStarredOverride,
   } = usePlayerStore();
   const { lastfmSessionKey } = useAuthStore();
+  const serverId = useAuthStore(s => s.activeServerId ?? '');
 
   const isRadio = !!currentRadio;
 
@@ -207,7 +209,10 @@ export default function PlayerBar() {
           <>
             <span className="player-time">{formatTime(currentTime)}</span>
             <div className="player-waveform-wrap">
-              <WaveformSeek trackId={currentTrack?.id} />
+              <WaveformSeek
+                trackId={currentTrack?.id}
+                url={currentTrack ? resolvePlaybackUrl(currentTrack.id, serverId) : undefined}
+              />
             </div>
             <span className="player-time">{formatTime(duration)}</span>
           </>