perf: round 14 — faces narrow projection, auth per-request allocs, CalDAV emit buffers, frontend set churn

Benchmark-gated (benches/ROUND14.md); every change ships a BEFORE/AFTER
benchmark with an equivalence gate and is rolled back on regression (the
rule is encoded as a GATE FAIL exit / threshold expect).

Backend
- Q1 faces_for_file → narrow face_boxes_for_file(id, person_id, bbox) with the
  caller filter pushed into SQL: drops the 2 KiB embedding BYTEA + 6 unused
  columns per face. 15-face lightbox open 0.312→0.219 ms, 32 KB→840 B/req.
- A1 cookie auth uses the borrow-only extract_cookie_str (already backs CSRF)
  instead of extract_cookie_value's owned String: -1 alloc/cookie request.
- A2 compute_relevance ASCII case-fold fast path vs name.to_lowercase() per
  result row (Unicode fallback preserved): 1.40x, 12→3 allocs/page.
- A3 sub pre-parsed to Uuid at decode time (TokenClaims.sub_id) vs re-parsing
  the 36-char claim on every request incl. cache hits: 22.7→0.7 ns.
- A4 auth + NextCloud middlewares borrow request.headers() instead of taking
  axum's HeaderMap extractor (a full map clone): 2→0 allocs/authed request.
- A5 CalDAV getlastmodified via the stack rfc2822_utc (byte-identical to
  chrono) vs a per-event to_rfc2822() heap String: 5→0 allocs.
- A6 CalDAV per-event href + quoted etag written into reused page buffers vs a
  fresh format! pair per event: 3.48x, 240→6 allocs/40-event page.

Frontend
- F1 t() shares one frozen EMPTY_PARAMS for the no-interpolation call forms vs
  a throwaway {} per call: -1 alloc/call.
- F2 favorites favoriteIds is a persistent SvelteSet with per-page add (clear
  on reset) vs a brand-new set over the whole accumulated list each page:
  22.3x over a 40-page drain (O(N^2)→O(N)).

Verified: cargo check --all-targets, cargo clippy -D warnings, both bench
packs (GATE PASS), frontend npm run check + vitest (4/4). ROUND14.md also
records the investigated-but-deferred backlog (music N+1, contact vcard
over-fetch, CachedBlobBackend syscalls, ResourceList.sections builder, etc.).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PymgCdK78NzUF3oRAQCJfN

src/interfaces/nextcloud/basic_auth_middleware.rs

@@ -1,6 +1,6 @@
 use axum::{
     extract::{Request, State},
-    http::{HeaderMap, StatusCode, header},
+    http::{StatusCode, header},
     middleware::Next,
     response::{IntoResponse, Response},
 };
@@ -70,13 +70,16 @@ impl IntoResponse for NextcloudAuthError {
 
 pub async fn basic_auth_middleware(
     State(state): State<Arc<AppState>>,
-    headers: HeaderMap,
     mut request: Request,
     next: Next,
 ) -> Result<Response, NextcloudAuthError> {
     tracing::debug!("[NC] {} {}", request.method(), request.uri());
 
-    let auth_header = headers
+    // Borrow the Authorization header directly rather than cloning the whole
+    // HeaderMap per NC sync request; the borrow ends at `parse_basic_auth`
+    // below, before any request mutation (benches/ROUND14.md §A4).
+    let auth_header = request
+        .headers()
         .get(header::AUTHORIZATION)
         .and_then(|value| value.to_str().ok())
         .ok_or_else(|| {