perf: round 22 — hot-GET HeaderMap borrow, native-WebDAV/CalDAV etag borrowed quotes, FileDto content_hash move, CalendarEvent stamp, ShareItemType case-fold

Benchmark-gated, same rule as ROUND2-21: every change ships with a
BEFORE/AFTER counting-allocator benchmark and a byte/-value equivalence
gate; an AFTER that fails to reduce allocations exits non-zero (rollback).
See benches/ROUND22.md and examples/bench_round22_micro.rs. All arms
no-Postgres.

- H1: the hot GET handlers (get_thumbnail, download_file, list_files_query,
  list_photos, NextCloud preview, public-share download/access) take
  `req: Request` last and read `req.headers()` by borrow instead of axum's
  HeaderMap extractor, whose FromRequestParts impl clones the whole request
  header table just to read 1-3 headers (the ROUND14 §A4 middleware pattern,
  finally propagated to the handlers). 2 -> 0 allocs/req · 9.95x wall.
- W1: native WebDAV write_etag_quoted — the etag emitter for every /webdav/
  PROPFIND row (per file AND per folder, up to 500/page) — emits the quotes
  as borrowed pre-escaped " text events instead of escaping a "{etag}"
  String (the ROUND20 §C1 / ROUND21 §R4 pattern). 3 -> 0 allocs/row.
- C1: CalDAV getetag routed through a shared write_quoted_etag helper across
  all 5 sites (3 per-event + 2 per-calendar); the now-dead etag: &mut String
  buffer threaded through write_event_response/standard/requested props + the
  two per-page buffers removed. 2 -> 0 allocs/row.
- D1: FileDto::from reuses the moved parts.blob_hash instead of cloning it
  via the content_hash() getter (the ROUND19/20 move-not-clone sweep missed
  it — hash/etag are read before into_parts()). Per file row of every
  listing. 1 -> 0 allocs/row.
- E1: CalendarEvent::update_time_range/update_all_day stamp timed
  DTSTART/DTEND via fmt::compact_ical_utc stack render (chrono fallback out
  of range) instead of the %Y%m%dT%H%M%SZ strftime interpreter. 4 -> 0.
- S1: ShareItemType::try_from uses eq_ignore_ascii_case instead of a
  throwaway to_lowercase() String. 1 -> 0 allocs/parse.

Verified: cargo clippy --features bench --all-targets -D warnings clean,
cargo fmt --all --check clean, cargo test --lib --features bench = 529
passed / 0 failed (incl. the OpenAPI-spec-validity test guarding the H1
utoipa-handler signature change).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DKyQ4AnYtgp1JtjzweyMeo

Cargo.toml

@@ -354,6 +354,22 @@ name = "bench_micro_allocs"
 path = "examples/bench_micro_allocs.rs"
 required-features = ["bench"]
 
+# Round-22 battery ────────────────────────────────────────────────────────────
+
+# Round-22 CPU/alloc micro-pack — the deferred hot-GET-handler `HeaderMap`
+# extractor clone (thumbnail/list/download/photos/preview/share read 1–3 headers
+# out of a full `parts.headers.clone()`), routed through `Request` + borrow (H1);
+# native-WebDAV `write_etag_quoted` borrowed pre-escaped quotes, the sweep's last
+# per-row DAV site (W1); CalDAV `getetag` shared `write_quoted_etag` helper across
+# 5 sites + dead etag-buffer removal (C1); `FileDto::from` reuse of the moved
+# `blob_hash` instead of the getter clone the move-not-clone sweep missed (D1);
+# `CalendarEvent` timed DTSTART/DTEND via `fmt::compact_ical_utc` (E1);
+# `ShareItemType::try_from` `eq_ignore_ascii_case` (S1). No Postgres.
+[[example]]
+name = "bench_round22_micro"
+path = "examples/bench_round22_micro.rs"
+required-features = ["bench"]
+
 # Round-21 battery ────────────────────────────────────────────────────────────
 
 # Round-21 CPU/alloc micro-pack — CalDAV/CardDAV row-mapper container pre-size