feat(now-playing): mount real waveform visualizer in NowPlaying card (mode C) + Fill container-sizing mode

Replace the 20 synthetic bars with a contained WaveformVisualizer driven by the live player, pointed at the current track; add a Fill mode (CSS-only, defaults off) sizing the canvas to its container; place the lava-lamp icon to popover on the card.

DeepDrftPublic.Client/Controls/NowPlayingCard.razor.css

@@ -1,8 +1,3 @@
-@keyframes wave-dance {
-    from { height: var(--h-lo, 4px); }
-    to { height: var(--h-hi, 20px); }
-}
-
 @keyframes blink {
     0%, 100% { opacity: 1; }
     50% { opacity: 0.3; }
@@ -51,22 +46,25 @@
     letter-spacing: 0.08em;
 }
 
-.waveform-bars {
-    display: flex;
-    align-items: center;
-    gap: 3px;
+/* Contained visualizer region (Phase 12 mode C). The visualizer mounts with Fill="true", whose
+   layer is `position: absolute; inset: 0` — so this box must be a positioned, sized ancestor for the
+   canvas to fill. `overflow: hidden` keeps the lava inside the card's rounded chrome. The height is the
+   card's bounded live readout — taller than the old synthetic-bar strip so the real waveform reads, but
+   still compact for a home-page hero panel. */
+.np-visualizer {
+    position: relative;
+    height: 120px;
     margin-top: 1.2rem;
-}
-
-.waveform-bar {
-    width: 3px;
-    background: var(--deepdrft-green-accent);
+    overflow: hidden;
     border-radius: 2px;
-    animation: wave-dance var(--dur, 1s) ease-in-out infinite alternate;
 }
 
-.waveform-placeholder {
-    margin-top: 1.2rem;
-    height: 1px;
-    background: rgba(250, 250, 248, 0.12);
-}
+/* The lava-lamp popover trigger overlays the visualizer's top-right corner (full parity, §8e). Above
+   the canvas (z-index) and pointer-enabled so the icon is clickable even though the canvas layer below
+   it is pointer-events:none. */
+.np-visualizer-controls {
+    position: absolute;
+    top: 0.25rem;
+    right: 0.25rem;
+    z-index: 1;
+}