Live worker counts and an e621 request-history dropdown

- Status polling drops from 30s to 5s, and download start/finish/cancel
  invalidates it immediately, so the footer's Active Workers reflects
  running download tasks in near real time
- The e621 time in the status pill is now a button: it opens a dropdown
  with the session's request history (clock time, endpoint, duration,
  colour-coded) plus totals; closes on outside click or Escape
- Metrics store keeps the last 50 requests

ROADMAP.md

@@ -21,10 +21,13 @@ they land.
 
 ## 2. e621 integration
 
-- [ ] **Download progress bar on the detail view**
-  - [ ] Backend download task model (status, progress %, downloaded/total bytes, speed)
-  - [ ] Progress endpoint the SPA polls; cancel support
-  - [ ] Frontend progress bar with speed and cancel on `/detail/<post>`
+- [x] **Download progress bar on the detail view**
+  - [x] Backend download task (status, progress %, downloaded/total bytes, speed)
+  - [x] Progress endpoint the SPA polls; cancel support
+  - [x] Frontend progress bar with speed and cancel on `/detail/<post>`
+  - [x] The status footer's "Active Workers" now counts running download tasks
+- [x] **Download to client** — streams the e621 original straight to the
+      browser (works for guests; host-restricted proxy, no library write)
 - [ ] **Match local files to e621**
   - [ ] Match by MD5 from the library detail (manual post ID entry)
   - [ ] Batch cache status for the whole library (`matched` / `not_found` / `deleted`)