feat(public-nav): slim appbar to ARCHIVE + inline CUTS/SESSIONS/MIXES, drop GENRES and Tracks (8.I)

Desktop flattens the ARCHIVE popover into inline appbar links above the medium
breakpoint; mobile keeps the indented sub-list under ARCHIVE. GENRES and /tracks
removed from nav only — routes (GenresView, TracksView) remain reachable by URL.
Retires the now-dead desktop hover-popover and its 8.J collapse-state machinery
(mobile drawer still dismisses on click).

DeepDrftPublic.Client/Layout/DeepDrftMenu.razor.css

@@ -82,66 +82,6 @@
     color: var(--deepdrft-white);
 }
 
-/* Dual-role parent node: anchor for the parent route, positioning context for the dropdown. */
-.dd-nav-item-parent {
-    position: relative;
-}
-
-/* Hover-revealed child dropdown. Pure CSS — hidden by default, shown when the parent item is
-   hovered or contains keyboard focus. Sits directly beneath the parent link, frosted to match
-   the bar. */
-.dd-nav-dropdown {
-    position: absolute;
-    top: 100%;
-    left: 50%;
-    transform: translateX(-50%) translateY(0.25rem);
-
-    display: flex;
-    flex-direction: column;
-    align-items: stretch;
-    gap: 0.75rem;
-
-    list-style: none;
-    margin: 0;
-    padding: 1rem 1.5rem;
-    min-width: 9rem;
-
-    background: rgba(250, 250, 248, 0.96);
-    border: 1px solid var(--deepdrft-border);
-    -webkit-backdrop-filter: blur(18px);
-    backdrop-filter: blur(18px);
-
-    opacity: 0;
-    visibility: hidden;
-    pointer-events: none;
-    transition: opacity 0.18s ease, visibility 0.18s ease;
-    z-index: 101;
-}
-
-.dd-nav-dark .dd-nav-dropdown {
-    background: rgba(13, 13, 18, 0.95);
-}
-
-.dd-nav-item-parent:hover .dd-nav-dropdown,
-.dd-nav-item-parent:focus-within .dd-nav-dropdown {
-    opacity: 1;
-    visibility: visible;
-    pointer-events: auto;
-}
-
-/* Force-close the dropdown immediately after a child link is clicked (SPA navigation
-   keeps the DOM and :hover may remain true). Cleared on mouseleave so the next
-   hover cycle works normally. */
-.dd-nav-item-parent.dd-nav-item-collapsed .dd-nav-dropdown {
-    opacity: 0 !important;
-    visibility: hidden !important;
-    pointer-events: none !important;
-}
-
-.dd-nav-dropdown-link {
-    white-space: nowrap;
-}
-
 /* Right-side cluster */
 .dd-nav-actions {
     display: flex;