perf: round 7 — photos timeline O(N²)→incremental, range-seek authz duplication, resources row-map clone

Benchmark-gated (equivalence + BEFORE/AFTER; results + reproduce commands in
benches/ROUND7.md):

- Photos timeline re-grouped + re-laid-out the whole accumulated library on
  every 60-item page (both `groups` and `photoRows` were $derived over the
  full list), Σ ≈ O(N²/60) main-thread work during a scroll. Pages arrive
  newest-first so grouping is append-only: the new PhotoTimeline
  (lib/utils/photoTimeline.ts) re-buckets only the fresh page and re-lays-out
  only changed groups, reusing untouched groups' cached rows, falling back to
  a full rebuild on any config/deletion/non-append change. The pure
  buildPhotoRows is the verbatim reference the gate holds it equal to at every
  page. 50×60 drain: 76 500 → 3 000 grouping ops (25.5x), 23.0 → 2.2 ms
  (10.6x).

- Range downloads paid authz + access-notify twice: download_file_impl
  resolves the file via get_file_with_perms, then the Range branch re-ran
  require_file + notify_file_accessed per request. Media/PDF viewers fetch
  exclusively via Range (one request per seek), so every seek in a scrub
  re-authorized an already-cleared file. Now routed through the non-perms
  get_file_range_preloaded (matching the share-landing + WebDAV range paths);
  the unused _with_perms range method is removed. The request-level gate still
  denies before the branch runs (bench asserts member granted, outsider
  denied). Per seek removed: WARM 0.67 µs, COLD 1362.66 µs — a grant-cascade
  drive-resolve query per seek for a shared-drive recipient on a cold cache.

- /api/folders/{id}/resources row→DTO mapping cloned row.name into the DTO
  though the row is owned; folders move it (fixed icons), files compute the
  name-derived icon/category classes first then move it. 500-row page:
  10.004 → 9.004 allocs/row (500 clones removed), output identical.

Deferred with rationale in ROUND7.md: thumbnail ACL-before-304 (security
posture — needs a security review, not a perf tweak), batch_operations
Arc<str>→String widening, list-view O(N²) on smaller lists, and the serial→
join! pairs (decide-by-bench with injected latency, per the round-6 rejection).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017aJu9ghvuT8WqC31ZEGTBA

src/application/services/file_retrieval_service.rs

@@ -287,22 +287,6 @@ impl FileRetrievalService {
         Ok(files.into_iter().map(FileDto::from).collect())
     }
 
-    /// Range read that first consults the RAM content cache (see
-    /// [`Self::get_file_range_preloaded`]).
-    pub async fn get_file_range_preloaded_with_perms(
-        &self,
-        dto: &FileDto,
-        caller_id: Uuid,
-        start: u64,
-        end: Option<u64>,
-    ) -> Result<RangeContent, DomainError> {
-        self.require_file(&dto.id, Permission::Read, caller_id)
-            .await?;
-        // Same throttled Recent recording as the streaming variant.
-        self.notify_file_accessed(caller_id, &dto.id);
-        self.get_file_range_preloaded(dto, start, end).await
-    }
-
     /// Range read for HTTP Range Requests, cache-aware.
     ///
     /// Media players and PDF viewers fetch these files *exclusively* through