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).

hive-ag3nt/src/web_ui.rs

@@ -539,8 +539,13 @@ async fn api_loose_ends(State(state): State<AppState>) -> Response {
 /// fail the whole list.
 async fn api_bash_tasks() -> Response {
     let dir = crate::paths::harness_dir().join("bash-tasks");
-    let mut tasks: Vec<hive_sh4re::TaskFile> = Vec::new();
-    if let Ok(rd) = std::fs::read_dir(&dir) {
+    // The dir scan + per-file reads are blocking fs I/O; run them off the
+    // async executor so a slow or large tasks dir can't stall other requests.
+    let tasks = tokio::task::spawn_blocking(move || {
+        let mut tasks: Vec<hive_sh4re::TaskFile> = Vec::new();
+        let Ok(rd) = std::fs::read_dir(&dir) else {
+            return tasks;
+        };
         for entry in rd.flatten() {
             let path = entry.path();
             if path.extension().and_then(|e| e.to_str()) != Some("json") {
@@ -559,17 +564,20 @@ async fn api_bash_tasks() -> Response {
                 tasks.push(task);
             }
         }
-    }
-    // Running before Pending, then oldest-first so a long-runner sits on top.
-    tasks.sort_by(|a, b| {
-        let rank = |s: &hive_sh4re::TaskStatus| match s {
-            hive_sh4re::TaskStatus::Running => 0,
-            _ => 1,
-        };
-        rank(&a.status)
-            .cmp(&rank(&b.status))
-            .then(a.created_at.cmp(&b.created_at))
-    });
+        // Running before Pending, then oldest-first so a long-runner sits on top.
+        tasks.sort_by(|a, b| {
+            let rank = |s: &hive_sh4re::TaskStatus| match s {
+                hive_sh4re::TaskStatus::Running => 0,
+                _ => 1,
+            };
+            rank(&a.status)
+                .cmp(&rank(&b.status))
+                .then(a.created_at.cmp(&b.created_at))
+        });
+        tasks
+    })
+    .await
+    .unwrap_or_default();
     axum::Json(serde_json::json!({ "tasks": tasks })).into_response()
 }