Phase 9 Wave 4: ARCHIVE nav + Cuts/Sessions/Mixes pages + MixWaveformVisualizer

Replaces flat RELEASES/SESSIONS/MIXES nav with ARCHIVE dropdown (PageRoute.Children,
one-level cap, dual-role node). Adds /archive overview, /cuts (AlbumsView + medium
filter; /albums redirects), /sessions + /sessions/{id} (hero-dominant), /mixes +
/mixes/{id} (MixWaveformVisualizer full-page background). Extracts ReleaseDetailScaffold
from TrackDetail (invariant trio). PersistentComponentState bridge on all new pages.
Click-to-seek seam designed on MixWaveformVisualizer (inert until wired).

DeepDrftPublic.Client/Controls/MixWaveformVisualizer.razor.css

@@ -0,0 +1,31 @@
+/* Full-viewport fixed backdrop. Sits behind page content (negative-ish z-index within the
+   detail layout) and never intercepts pointer events until click-to-seek ships. */
+.mix-waveform-bg {
+    position: fixed;
+    inset: 0;
+    z-index: 0;
+    pointer-events: none;
+    overflow: hidden;
+    display: flex;
+    align-items: center;
+}
+
+.mix-waveform-bg--empty {
+    /* No datum: nothing to draw. Kept as a hook for a future flat-line fallback. */
+}
+
+.mix-waveform-svg {
+    width: 100%;
+    height: 60vh;
+    margin: auto 0;
+    opacity: 0.18;
+}
+
+/* Native SVG elements — scoped CSS stamps these directly, no ::deep needed. */
+.mix-waveform-fill {
+    fill: var(--mud-palette-text-secondary);
+}
+
+.mix-waveform-played {
+    fill: var(--mud-palette-primary);
+}