perf: round 19 — auth/WOPI/vCard/PROPFIND per-request & per-row alloc cuts

Benchmark-gated (examples/bench_round19_micro.rs, benches/ROUND19.md): every
section ships a BEFORE/AFTER counting-allocator arm with a byte/-value
equivalence gate and a GATE-FAIL-rollback exit. All eight pass. No Postgres.

- M1 verify_basic_auth cache key: blake3::hash(format!("{u}:{p}")) → incremental
  Hasher (byte-identical key, 2→0 allocs on every Basic-auth DAV request)
- M2 WopiTokenService: prebuild Validation/DecodingKey/EncodingKey in new()
  instead of per-call (mirrors JwtTokenService; 16→12 allocs/validate)
- V1/V2 vCard emit (contact_to_vcard/generate_vcard): FN fallback drops the
  throwaway to_string, NOTE skips the escape copy for newline-free notes, REV
  uses new common::fmt::compact_ical_utc stack renderer (11.5× vs chrono
  strftime, 3→0 allocs); per-contact 9→4 allocs
- M4 trash_service::row_to_item_dto: move name/path/blob_hash out of the owned
  row instead of cloning (3 clones/file row gone)
- M5 search cache key: Uuid::hyphenated().encode_lower stack buffer instead of
  to_string (identical u64 key, 1→0 allocs/request)
- M6 streaming PROPFIND: reuse one href buffer across the page instead of a
  format! per child (native + NC handlers; 192→3 allocs on a 64-child page)
- M7 nextcloud extract_url_user: return Cow instead of forcing into_owned
  (zero-alloc on the common ASCII-username path)

common::fmt::compact_ical_utc added with chrono-parity unit tests (CASES +
60-year sweep). cargo fmt + clippy --all-targets clean; 526 lib unit tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ront9bk7YMoffVQkGG47gh

src/application/services/contact_service.rs

@@ -339,12 +339,22 @@ impl ContactService {
             let _ = write!(vcard, "BDAY:{}\r\n", birthday.format("%Y%m%d"));
         }
 
-        // Revision (last update)
-        let _ = write!(
-            vcard,
-            "REV:{}\r\n",
-            contact.updated_at().format("%Y%m%dT%H%M%SZ")
-        );
+        // Revision (last update) — stack renderer, see benches/ROUND19.md §V2.
+        let mut rev_buf = [0u8; 16];
+        match crate::common::fmt::compact_ical_utc(&mut rev_buf, contact.updated_at().timestamp()) {
+            Some(rev) => {
+                vcard.push_str("REV:");
+                vcard.push_str(rev);
+                vcard.push_str("\r\n");
+            }
+            None => {
+                let _ = write!(
+                    vcard,
+                    "REV:{}\r\n",
+                    contact.updated_at().format("%Y%m%dT%H%M%SZ")
+                );
+            }
+        }
 
         vcard.push_str("END:VCARD\r\n");