perf: implement findings #2, #3, #17 from architecture audit

- Finding #2: Replace Mutex<HashMap> with moka::sync::Cache in file_blob_read_repository (10K cap, 30s TTI)
- Finding #3: Add chunked upload persistence with session.json + progress.bin bitmask for crash recovery
- Finding #17: Remove manual gzip compression, delegate entirely to tower-http CompressionLayer
- Remove dead code: StubCompressionPort, GzipCompressionService re-export, duplicate response structs
- All 114 tests passing

src/interfaces/api/routes.rs

@@ -358,7 +358,9 @@ pub fn create_api_routes(app_state: &AppState) -> Router<AppState> {
     let admin_router = admin_handler::admin_routes().with_state(app_state.clone());
     router = router.nest("/admin", admin_router);
 
-    // Compression for API responses (JSON) — excludes file downloads
+    // Transparent compression (gzip + brotli) for all API responses.
+    // tower-http negotiates via Accept-Encoding and skips already-compressed
+    // content types automatically. No manual compression in handlers.
     router
         .layer(CompressionLayer::new().br(true).gzip(true))
         .layer(TraceLayer::new_for_http())