fix(web/m7-365): align /library/history with albums-page conventions

Code-quality review flagged convention drift from sibling library
pages. Aligning so the history page matches the same shape:

- queryStore + $derived($queryStore) pattern (single subscription
  point) instead of $query.X everywhere.
- h1 uses font-display text-2xl font-medium per FabledSword design
  system (weights 400/500 only — font-semibold drifted to 600).
- h2 uses font-medium + z-10 for sticky-header layering.
- InfiniteScrollSentinel uses its `enabled` prop (which exists; the
  earlier spec note claiming otherwise was wrong) so the observer
  isn't recreated on every fetch cycle.
- Loading more… / End of history footers added to match albums.
- onRetry passes query.refetch by reference, not wrapped.
- Dropped redundant `as HistoryEvent[]` cast.

Also fixed test case 4 which trivially passed regardless of the
conditional gate's correctness — now queries the sentinel's actual
DOM root (div[aria-hidden="true"].h-px) and asserts presence/absence.
Added a positive twin test for hasNextPage=true.

web/src/routes/library/history/page.test.ts

@@ -108,10 +108,18 @@ describe('library/history page', () => {
     mockData = { pages: [{ events: [mkEvent('a', new Date())], has_more: false }] };
     mockHasNextPage = false;
     const { container } = render(HistoryPage);
-    // Sentinel renders an empty <div ref> — assert by absence of the call.
-    // (We can't easily query for the sentinel itself in the DOM since it has
-    // no aria role; instead, verify the page renders the song without error.)
+    // InfiniteScrollSentinel renders <div aria-hidden="true" class="h-px">.
+    // When hasNextPage is false, no such div should be in the DOM.
+    expect(container.querySelector('div[aria-hidden="true"].h-px')).toBeNull();
+    // Confirm the page rendered the row so we know we hit the success branch.
     expect(screen.getByText('Song a')).toBeInTheDocument();
-    expect(container).toBeTruthy();
+  });
+
+  it('renders the InfiniteScrollSentinel when hasNextPage is true', () => {
+    mockData = { pages: [{ events: [mkEvent('a', new Date())], has_more: true }] };
+    mockHasNextPage = true;
+    mockIsFetchingNextPage = false;
+    const { container } = render(HistoryPage);
+    expect(container.querySelector('div[aria-hidden="true"].h-px')).not.toBeNull();
   });
 });