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/Pages/AlbumsRedirect.razor

@@ -0,0 +1,10 @@
+@page "/albums"
+@inject NavigationManager Navigation
+
+@* Cuts replaced the standalone /albums route in Phase 9. Old links keep working via a
+   permanent redirect to /cuts rather than 404ing. *@
+
+@code {
+    protected override void OnInitialized()
+        => Navigation.NavigateTo("/cuts", forceLoad: false, replace: true);
+}