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

src/infrastructure/repositories/pg/calendar_pg_repository.rs

@@ -16,6 +16,24 @@ impl CalendarPgRepository {
     pub fn new(pool: Arc<PgPool>) -> Self {
         Self { pool }
     }
+
+    /// `EXISTS` short-circuit for the login provisioning hook, which only
+    /// needs to know whether the user owns ANY calendar. The old
+    /// `list_calendars_by_owner(..).is_empty()` hydrated every owned
+    /// `Calendar` row (8 cols incl. description/color TEXT) on EVERY login
+    /// just to test emptiness — the ROUND9 §7 `Drive::is_empty` COUNT→EXISTS
+    /// pattern (benches/ROUND13.md §Q2).
+    pub async fn has_owned_calendar(&self, owner_id: Uuid) -> CalendarRepositoryResult<bool> {
+        let exists: bool =
+            sqlx::query_scalar("SELECT EXISTS(SELECT 1 FROM caldav.calendars WHERE owner_id = $1)")
+                .bind(owner_id)
+                .fetch_one(&*self.pool)
+                .await
+                .map_err(|e| {
+                    DomainError::database_error(format!("Failed to probe owned calendars: {}", e))
+                })?;
+        Ok(exists)
+    }
 }
 
 impl CalendarRepository for CalendarPgRepository {