bash-tasks page: live interval poll + spawn_blocking the dir scan (review)

Two fixes from review:
- Liveness: /api/state isn't polled while online (only during login), so
  hooking refreshBashTasks to it only populated on cold load. Bash tasks
  start + finish asynchronously between turns, so add a light ~4s interval
  to keep the tasks pill live; the /api/state-time call now just does the
  first-paint populate. Doc note corrected to match.
- Move the blocking dir scan + per-file reads in /api/bash-tasks off the
  async executor via tokio::task::spawn_blocking (damocles nit).

frontend/packages/agent/src/app.js

@@ -1354,9 +1354,11 @@ window.marked = marked;
       // db, fetched via the per-agent socket). Cold-load fetches
       // it here; turn_end refreshes it via the renderer below.
       refreshLooseEnds();
-      // Running bash tasks live in the in-container bash-tasks dir (not
-      // /api/state); same poll cadence as loose-ends. They complete async
-      // between turns, so polling on each state cycle keeps the count live.
+      // Cold-load populate of the running-bash-tasks pill. Tasks complete
+      // asynchronously between turns (independent of turn_end SSE) and
+      // /api/state isn't polled while online, so a dedicated interval (set
+      // up next to the initial refreshState() below) keeps the count live;
+      // this call just fills it immediately on first paint.
       refreshBashTasks();
       // Skip the re-render if nothing structurally changed. The most
       // common case is `online` polling itself — without this guard, the
@@ -1387,6 +1389,12 @@ window.marked = marked;
     }
   }
   refreshState();
+  // Keep the running-bash-tasks pill live. Unlike loose-ends (refreshed on
+  // turn_end SSE), bash tasks start + finish asynchronously between turns and
+  // /api/state isn't polled while online — so poll the cheap snapshot endpoint
+  // on a light interval. Fails silently (renders zero) when offline. v1 is
+  // polling; an SSE push for task state could replace this later.
+  setInterval(refreshBashTasks, 4000);
 
   // ─── live event stream ──────────────────────────────────────────────────
   // Scrolling, pill, backfill + SSE plumbing live in hive-fr0nt::TERMINAL_JS