chore: v2.8.12 — clone queue and progress, session defaults, chat agents, drops as @ mentions

Whole tree from parallel sessions, plus the version bump:
- Clone: a queue with live progress (Add workspace and extra folders),
  clones run under nice/ionice so the machine stays responsive.
- Settings → AI tools → Session defaults: a new session's default
  permission mode / bypass per account.
- Chat lists the background subagents that have not reported back yet.
- A file pasted or dropped into a claude pane goes in as an @ mention.
- Changes panel: say why amend/undo is refused on a pushed commit.
- openapi.yaml regenerated (Artifacts, Host, resumeById).

server/__tests__/api.test.js

@@ -100,6 +100,9 @@ const EXPECTED_API_PATHS = [
   "/api/webhooks/{id}",
   "/api/webhooks/{id}/test",
   "/api/webhooks/{id}/deliveries",
+  "/api/artifacts",
+  "/api/artifacts/{id}/install",
+  "/api/host",
   "/api/openapi.json",
   "/api/docs",
   "/api/redoc",