chore: v2.8.21 — update progress steps, clone in background, extra SSH keys inline, today's spend

- Plugin update reports its running step (plugin-update-progress.json →
  plugin_update_progress); a hidden update or clone leaves a progress chip.
- Clone here can run in the background.
- Git identity: extra SSH keys are added inline per host (no More keys tab).
- Users: spend today (viewer's local day, ?tz_offset=).
- Prettier on the files touched since v2.8.20.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "agenthub",
-  "version": "2.8.20",
+  "version": "2.8.21",
   "bin": {
     "agenthub": "bin/agenthub.js"
   },