perf: serve ranges from RAM cache, stream ZIPs, overlap ingest settle, O(1) chunk gate

Round 2 of benchmark-gated optimizations (benches/ROUND2.md; every change
gated by a before/after in examples/bench_round2.rs — an AFTER that did
not beat its BEFORE was to be rolled back; none needed it):

- Range requests (REST/DAV/shares) answered from the moka content cache
  for sub-10MB files: PG resolve + open/seek/read -> Bytes::slice.
  256KiB seeks: 1,730/s -> 3.7M/s (p50 552us -> 0.15us).
- Streaming folder/share ZIPs via tokio duplex: TTFB no longer scales
  with archive size (326ms -> 0.4ms on 192MiB corpus; total also faster).
  Content-Length dropped (size unknown up front).
- NC chunked-upload per-PUT gate: O(k) directory scan+stat -> in-RAM
  per-session counter (lazy rebuild on cold start). 1,000-chunk upload
  gate cost: 33.1s -> 0.09s cumulative.
- Delta download + commit-verify now use the CDC path's
  buffered(read_prefetch) read-ahead: 64-chunk drain at 5ms open
  latency 440ms -> 51ms; order preserved.
- CDC ingest settles batches on a spawned task (depth-1 pipeline) so
  the source stream keeps flowing during PG pin + backend writes;
  rollback ledger shared + lock-serialized so compensation stays exact
  on cancellation. 512MiB paced ingest: 60-69 -> 74-75 MB/s.
  OXICLOUD_INGEST_OVERLAP=0 restores inline settling (ops/bench hatch).
- Frontend: instant-upload BLAKE3 hashing moved off the main thread to
  a bounded Web Worker pool (File handles by reference); vitest gate
  asserts the pool beats sequential (first gate draft posting buffers
  was 2.6x slower and was rewritten — copies dominated).

Validation: cargo fmt + clippy -D warnings clean; 514 unit + 544
integration tests green; 270 frontend tests green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CBK1RdtzyP6759Muqe1K1w

src/application/ports/file_ports.rs

@@ -111,6 +111,17 @@ pub enum OptimizedFileContent {
     Stream(Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>),
 }
 
+/// Result of a cache-aware HTTP-Range read
+/// (`FileRetrievalService::get_file_range_preloaded`). Same split as
+/// [`OptimizedFileContent`]: handlers map each variant onto a response body.
+pub enum RangeContent {
+    /// Zero-copy slice out of the RAM content cache (a `Bytes::slice` is a
+    /// refcount bump — no allocation, no I/O, no DB).
+    Bytes(Bytes),
+    /// Streaming range read from the blob store (cache miss / large file).
+    Stream(Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>),
+}
+
 /// Primary port for file retrieval operations
 pub trait FileRetrievalUseCase: Send + Sync + 'static {
     /// Gets a file by its ID (system/internal — no ownership check).