feat(cms): Release Archive medium tab strip (ALL · CUTS · SESSIONS · MIXES), retire navigate-away cards

Replace the navigate-away ReleaseArchiveBrowser cards and the redundant top-level Releases
toggle with an in-page MudTabs strip under the Releases mode: ALL (CmsAllReleasesGrid) plus
one enum-driven tab per ReleaseMedium. Sessions/Mixes browsers gain an Embedded flag that
suppresses standalone page chrome when hosted as tab content; CmsCutBrowser is the new
Cut-filtered grid. /tracks/sessions, /tracks/mixes, /tracks/archive stay reachable by URL.

DeepDrftManager/Components/Pages/Tracks/CmsMixBrowser.razor

@@ -5,25 +5,58 @@
 @attribute [Authorize]
 @inject ILogger<CmsMixBrowser> Logger
 
-<PageTitle>Mixes — DeepDrft CMS</PageTitle>
+@* Embedded as the MIXES tab content of the Release Archive (Phase 9 §8.A), and still routable at
+   /tracks/mixes for direct-URL access. When embedded, the page chrome (title, container, the now-
+   meaningless "Back to Release Archive" button) is suppressed — the host tab strip owns that frame; only
+   the grid renders. The standalone route keeps the full page chrome. The per-row waveform affordance
+   (9.5.E) is preserved in both contexts. *@
+@if (Embedded)
+{
+    @GridContent
+}
+else
+{
+    <PageTitle>Mixes — DeepDrft CMS</PageTitle>
 
-<MudContainer MaxWidth="MaxWidth.Large" Class="mt-8">
-    <MudButton Variant="Variant.Text"
-               StartIcon="@Icons.Material.Filled.ArrowBack"
-               Href="/tracks/archive"
-               Class="mb-4">
-        Back to Release Archive
-    </MudButton>
+    <MudContainer MaxWidth="MaxWidth.Large" Class="mt-8">
+        <MudButton Variant="Variant.Text"
+                   StartIcon="@Icons.Material.Filled.ArrowBack"
+                   Href="/tracks/archive"
+                   Class="mb-4">
+            Back to Release Archive
+        </MudButton>
 
-    <MudText Typo="Typo.h4" GutterBottom="true">Mixes</MudText>
+        <MudText Typo="Typo.h4" GutterBottom="true">Mixes</MudText>
 
-    <CmsMediumTable TRow="MixRow"
-                    Rows="Rows"
-                    Loading="Loading"
-                    ReleaseAccessor="@(row => row.Release)"
-                    ThumbUrl="@(key => ThumbUrl(key))"
-                    TitleHeader="Mix"
-                    EmptyMessage="No mixes found.">
+        @GridContent
+    </MudContainer>
+}
+
+@code {
+    /// <summary>
+    /// True when rendered as tab content inside the Release Archive; suppresses the standalone page
+    /// chrome (title, container, back button). False (default) renders the full routable page.
+    /// </summary>
+    [Parameter] public bool Embedded { get; set; }
+
+    protected override ReleaseMedium Medium => ReleaseMedium.Mix;
+    protected override string MediumNoun => "mixes";
+
+    protected override MixRow ToRow(ReleaseDto release) => new()
+    {
+        Release = release,
+        HasWaveform = !string.IsNullOrEmpty(release.MixMetadata?.WaveformEntryKey)
+    };
+
+    // The grid itself — identical in the embedded and standalone contexts. Defined once as a fragment so
+    // both branches above render the same markup without duplication.
+    private RenderFragment GridContent => @<CmsMediumTable TRow="MixRow"
+                                                           Rows="Rows"
+                                                           Loading="Loading"
+                                                           ReleaseAccessor="@(row => row.Release)"
+                                                           ThumbUrl="@(key => ThumbUrl(key))"
+                                                           TitleHeader="Mix"
+                                                           EmptyMessage="No mixes found.">
         <ActionContent Context="row">
             @if (row.HasWaveform)
             {
@@ -53,18 +86,7 @@
                 }
             </MudButton>
         </ActionContent>
-    </CmsMediumTable>
-</MudContainer>
-
-@code {
-    protected override ReleaseMedium Medium => ReleaseMedium.Mix;
-    protected override string MediumNoun => "mixes";
-
-    protected override MixRow ToRow(ReleaseDto release) => new()
-    {
-        Release = release,
-        HasWaveform = !string.IsNullOrEmpty(release.MixMetadata?.WaveformEntryKey)
-    };
+    </CmsMediumTable>;
 
     private async Task GenerateWaveformAsync(MixRow row)
     {