perf: round 13 — grouped-view virtualization, notification/login query narrowing, HTTP dedup, locale precompute

Benchmark-gated (BEFORE/AFTER + equivalence/safety gate per change), same
discipline as rounds 2-12. Full write-up in benches/ROUND13.md.

Shipped:
- V1 Grouped views windowed (files route + ResourceList). The grid arm was
  the last unwindowed path (trash is grouped-by-default in grid): each
  swimlane now feeds its own VirtualList, outer container a flex stack.
  vitest gate: 800-item grouped grid mounts <120 .file-item (was 800).
- Q1 get_users_by_ids drops the <=512 KiB avatar image + ui_preferences
  JSONB (notification path never reads them). 30-member fan-out 8.60 ->
  0.25 ms (34.3x), ~7.7 MB off the wire.
- Q2 Login provisioning is_empty() -> SELECT EXISTS for calendar + address
  book (every login). 0.193 -> 0.170 ms, widens with owned-row count.
- Q3 Recent-access prunes only when the upsert inserted (RETURNING xmax=0)
  — a re-access can't grow the set. 0.567 -> 0.324 ms (1.75x).
- L1 Locale supported-codes precomputed once vs rebuilt per anonymous
  request. 616 -> 17.3 ns (35.7x), 18 -> 1 allocs.
- H1 Duplicate /api TraceLayer removed (global stack already wraps it).
  1.86 -> 1.42 us/request, -6 allocs.
- H2 client_ip span field: borrow-only ClientIpDisplay vs owned String.
  187 -> 173 ns, -1 alloc.

Not shipped (discipline): the "media hooks read the blob 3x" lead was a
correctness bug, not a perf dup — the raw-path metadata/faces readers
resolve only for local+unencrypted+single-chunk blobs and silently produce
nothing otherwise. Flagged for maintainers; routing through read_blob_bytes
is a correctness fix (perf-neutral-to-negative), not a benchmark-gated
perf change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BfidAJD5AHw23jtvBUNamB

frontend/src/lib/styles/ported/resourceList.css

@@ -1025,6 +1025,25 @@
     margin-top: 0;
 }
 
+/* Grouped-grid container (files route): a vertical stack of
+   (header + its own windowed card grid) per swimlane. Not a grid itself —
+   the card grid rides each VirtualList's inner window — so it just stacks. */
+.files-grouped-grid {
+    display: flex;
+    flex-direction: column;
+}
+
+/* In that flex stack the `grid-column: 1 / -1` span is inert; the header
+   spans naturally as a block-level flex child. First header needs no top
+   margin (there is no list-header sibling before it in the grid path). */
+.files-grouped-grid > .resource-list__swimlane-header--grid {
+    grid-column: auto;
+}
+
+.files-grouped-grid > .resource-list__swimlane-header--grid:first-child {
+    margin-top: 0;
+}
+
 /* When the header contains a rich DOM node (e.g. a user vignette for the
    "owner" group-by), reset the typographic overrides that only make sense
    for plain-text labels, and lay the node out inline. */