fix(ui): full-width spectrum + log-mapped bars; deeper sepia + soft art fade

Spectrum
- Logarithmic frequency-to-bar mapping (squared time so bins
  stretch toward the highs). Per-bar high-end gain ramps from
  1.0x at the lowest bar to 3.0x at the highest, so the right
  half of the spectrum no longer reads as dead air.
- Floor bumped from 6% to 12% so silent bars stay visible.
- Skip bin 0 (DC + sub-rumble) which was overwhelming the lows.
- Use peak (not average) within each band — punchier visual.
- Container height 56→64, gradient now copper-lo → copper →
  copper-hi for more visible top tips. min-width: 0 / box-sizing
  border-box ensures the row truly claims the full grid column.
- Backend FFT path is unchanged: WS audio_data → setFrequencyData
  → renderVisualizerFrame → updateEditorialSpectrum. No
  client-side analyzer added.

Album art (vinyl label)
- Deeper sepia (0.35→0.6) and lower saturate (0.85→0.7) so
  vibrant covers blend into the copper grooves.
- Soft radial mask: outer ~22% of the disc fades toward the
  vinyl black so the album art dissolves into the surface
  rather than terminating at a hard clip edge.
- Hover state pulls the fade inward and eases sepia back so
  the user can still see the real cover at near-natural color.
- Glow tint matches the new sepia depth.

media_server/static/css/styles.css

@@ -6639,29 +6639,58 @@ footer .separator { color: var(--ink-ghost); margin: 0 8px; }
     display: block;
     border-radius: 50%;
     z-index: 2;
-    /* Vinyl-consistent tint: warm sepia + slight sharpen + subtle contrast.
-       Saturate pushed down so vibrant covers don't fight the copper palette. */
+    /* Heavy vinyl-consistent tint: deeper sepia + lower saturation
+       so vibrant covers blend with the copper grooves. */
     filter:
-        sepia(0.35)
-        saturate(0.85)
-        contrast(1.08)
-        brightness(0.95)
-        hue-rotate(-6deg);
-    transition: filter 320ms var(--ease);
+        sepia(0.6)
+        saturate(0.7)
+        contrast(1.12)
+        brightness(0.88)
+        hue-rotate(-8deg);
+    transition: filter 480ms var(--ease), -webkit-mask-image 480ms var(--ease);
+    /* Soft radial fade — the outer ~12% of the art fades to black so
+       the album image dissolves into the vinyl surface rather than
+       cutting hard at the circular clip edge. */
+    -webkit-mask-image: radial-gradient(circle at 50% 50%,
+        black 0%,
+        black 78%,
+        rgba(0,0,0,0.85) 88%,
+        rgba(0,0,0,0.4) 96%,
+        transparent 100%);
+            mask-image: radial-gradient(circle at 50% 50%,
+        black 0%,
+        black 78%,
+        rgba(0,0,0,0.85) 88%,
+        rgba(0,0,0,0.4) 96%,
+        transparent 100%);
 }
 .now-playing:hover .vinyl-label #album-art {
-    /* On hover, ease back toward natural color so users can see the real art */
+    /* On hover, ease back toward natural color and pull the fade
+       inward so more of the real cover is visible. */
     filter:
-        sepia(0.18)
-        saturate(0.95)
+        sepia(0.25)
+        saturate(0.92)
         contrast(1.05)
-        brightness(1)
-        hue-rotate(-3deg);
+        brightness(0.98)
+        hue-rotate(-4deg);
+    -webkit-mask-image: radial-gradient(circle at 50% 50%,
+        black 0%,
+        black 88%,
+        rgba(0,0,0,0.9) 95%,
+        rgba(0,0,0,0.5) 99%,
+        transparent 100%);
+            mask-image: radial-gradient(circle at 50% 50%,
+        black 0%,
+        black 88%,
+        rgba(0,0,0,0.9) 95%,
+        rgba(0,0,0,0.5) 99%,
+        transparent 100%);
 }
 
-/* Match the glow tint to the album art treatment */
+/* Match the glow tint and soft edge to the album art treatment */
 .now-playing .vinyl-label #album-art-glow {
-    filter: blur(22px) saturate(1.2) sepia(0.35) hue-rotate(-6deg);
+    filter: blur(22px) saturate(1.1) sepia(0.5) hue-rotate(-8deg);
+    opacity: 0.4;
 }
 
 /* Tonearm */
@@ -6836,29 +6865,34 @@ body.visualizer-active .now-playing .spectrogram-canvas {
     fill: currentColor;
 }
 
-/* ─── Spectrum bars (JS-injected; real audio when available) ─── */
+/* ─── Spectrum bars (JS-injected; real audio from backend FFT) ── */
 .now-playing .spectrum {
     display: flex;
     align-items: flex-end;
     justify-content: stretch;
     gap: 2px;
-    height: 56px;
+    height: 64px;
     margin: 36px 0 24px;
     width: 100%;
+    /* Force the spectrum to claim the full grid column width even
+       if siblings (meta-grid cells) report intrinsic widths. */
+    box-sizing: border-box;
+    min-width: 0;
 }
 .now-playing .spectrum span {
     display: block;
     flex: 1 1 0;
-    min-width: 2px;
-    background: linear-gradient(to top, var(--copper-lo), var(--copper-hi));
-    opacity: 0.9;
+    min-width: 0;
+    background: linear-gradient(to top, var(--copper-lo) 0%, var(--copper) 60%, var(--copper-hi) 100%);
+    opacity: 0.92;
     transform-origin: bottom;
     border-radius: 99px 99px 0 0;
     height: var(--bar-h, 40%);
     animation: sr-snap-bar 1.1s ease-in-out infinite;
     animation-delay: var(--bar-delay, 0s);
     animation-play-state: paused;
-    transition: height 80ms linear;
+    transition: height 60ms linear;
+    will-change: height;
 }
 :root[data-playstate="playing"] .now-playing .spectrum span {
     animation-play-state: running;