feat(albums): draw the album dropdown that was already being computed

Enter on an album card fetched the album's tracks over the IPC and ran
the whole split state machine (splitMode true, splitIndex measured
against the real container), then render() drew the single grid because
it never consulted splitMode; connectedCallback referenced
renderSplitGrid only to satisfy noUnusedLocals. perf.p2 files this as
dead code — it is the only route from the albums grid to track-details,
since a plain click navigates to the catalog page instead.

Two things it needed that the audit does not mention. The grid could
not scroll: .grid-scroll-container is the markup artists-view and
genres-view use, and cover-grid had the class with no rule for it, so
186984px of albums sat in a 772px box at 5000 albums, unreachable by
wheel, keyboard or scrollbar — and that is the element scroll-manager
saves and restores, so its scrollTop was permanently 0. And the shared
context menu was labelled 'Album actions' unconditionally, which nothing
could observe while a track menu was unreachable.

Both halves of the split grid carry the listbox semantics the single
grid gained in the ARIA pass.

CLAUDE.md

@@ -689,6 +689,37 @@ retained chars and cap in one eval, rather than the next session having
 to rebuild the twenty-four-search reproduction before it can tell
 whether the ceiling still holds.
 
+**Expanding an album shows its tracks, and the code to do it was
+written and never called.** `cover-grid`'s dropdown — the album's
+tracks drawn between the two halves of a split grid — was reachable
+only from Enter/Space on a focused card (a plain *click* navigates to
+`explore-album-details`), and that path fetched the tracks over the
+IPC, ran the whole split state machine and then rendered the single
+grid, because `render()` never consulted `splitMode`.
+`connectedCallback` referenced `renderSplitGrid` purely to satisfy
+`noUnusedLocals`. `perf.p2` files this as dead code in the bundle; it
+is the only route from the albums grid to `track-details`.
+
+Two things it needed that are not in the audit. **The grid could not
+scroll at all**: `.grid-scroll-container` is the same markup
+`artists-view` and `genres-view` use, and `cover-grid` had the class
+with *no rule for it*, so the container grew to its full content height
+inside an `overflow: hidden` host — 186 984 px of albums in a 772 px
+box at 5 000 albums, unreachable by wheel, keyboard or scrollbar, and
+invisible on the eight-album fixture. That is also the element
+`scroll-manager.ts` saves and restores, so its `scrollTop` was
+permanently 0; with a real scroller the manager works as designed
+(2891 preserved exactly across an expand). And the shared context-menu
+panel was **labelled "Album actions" unconditionally**, which nothing
+could observe while the only menu that could open on a track was
+unreachable.
+
+The manager **moves the scroll to reveal the dropdown** rather than
+preserving it — on a small library that is most of the way back to the
+top (80 → 4, with the content *taller* after, so it is not clamping).
+"The position is preserved" is the wrong assertion; "the dropdown is on
+screen" is the contract.
+
 **A list pays per row, and only while scrolling.** The track list's Art
 column rendered `CoverArtPath` — the original artwork — into a 24 px
 box while `CoverArtSmall` sat unused on the same model, and