Improve Active Workers table and recover stale tasks

Backend:
- Add _recover_stale_tasks() to reset tasks stuck in 'in_progress'
  from previous crashes (tasks >5 min old get reset to pending)
- Called automatically on startup

Frontend:
- Fix dark mode colors using CSS variables instead of hardcoded values
- Add elapsed time column showing how long task has been running
- Add spinning indicator next to package name
- Add status badge (Running/Stale?)
- Highlight stale tasks (>5 min) in amber
- Auto-updates every 5 seconds with existing refresh

backend/app/pypi_cache_worker.py

@@ -33,6 +33,45 @@ _cache_worker_running: bool = False
 _dispatcher_thread: Optional[threading.Thread] = None
 
 
+def _recover_stale_tasks():
+    """
+    Recover tasks stuck in 'in_progress' state from a previous crash.
+
+    Called on startup to reset tasks that were being processed when
+    the server crashed. Resets them to 'pending' so they can be retried.
+    """
+    db = SessionLocal()
+    try:
+        # Find tasks that have been in_progress for more than 5 minutes
+        # These are likely from a crashed worker
+        stale_threshold = datetime.utcnow() - timedelta(minutes=5)
+
+        stale_count = (
+            db.query(PyPICacheTask)
+            .filter(
+                PyPICacheTask.status == "in_progress",
+                or_(
+                    PyPICacheTask.started_at == None,
+                    PyPICacheTask.started_at < stale_threshold,
+                ),
+            )
+            .update(
+                {
+                    "status": "pending",
+                    "started_at": None,
+                }
+            )
+        )
+        db.commit()
+
+        if stale_count > 0:
+            logger.warning(f"Recovered {stale_count} stale in_progress tasks from previous crash")
+    except Exception as e:
+        logger.error(f"Error recovering stale tasks: {e}")
+    finally:
+        db.close()
+
+
 def init_cache_worker_pool(max_workers: Optional[int] = None):
     """
     Initialize the cache worker pool. Called on app startup.
@@ -47,6 +86,9 @@ def init_cache_worker_pool(max_workers: Optional[int] = None):
             logger.warning("Cache worker pool already initialized")
             return
 
+        # Recover any stale tasks from previous crash before starting workers
+        _recover_stale_tasks()
+
         workers = max_workers or settings.PYPI_CACHE_WORKERS
         _cache_worker_pool = ThreadPoolExecutor(
             max_workers=workers,