Add Active Workers table to Background Jobs dashboard

Shows currently processing cache tasks in a dynamic table with:
- Package name and version constraint being cached
- Recursion depth and attempt number
- Start timestamp
- Pulsing indicator to show live activity

Backend changes:
- Add get_active_tasks() function to pypi_cache_worker.py
- Add GET /pypi/cache/active endpoint to pypi_proxy.py

Frontend changes:
- Add PyPICacheActiveTask type
- Add getPyPICacheActiveTasks() API function
- Add Active Workers section with animated table
- Auto-refreshes every 5 seconds with existing data

backend/app/pypi_proxy.py

@@ -28,6 +28,7 @@ from .pypi_cache_worker import (
     enqueue_cache_task,
     get_cache_status,
     get_failed_tasks,
+    get_active_tasks,
     retry_failed_task,
     retry_all_failed_tasks,
 )
@@ -849,6 +850,25 @@ async def pypi_cache_failed(
     return get_failed_tasks(db, limit=limit)
 
 
+@router.get("/cache/active")
+async def pypi_cache_active(
+    limit: int = Query(default=50, ge=1, le=500),
+    db: Session = Depends(get_db),
+    _current_user: User = Depends(require_admin),
+):
+    """
+    Get list of currently active (in_progress) cache tasks.
+
+    Shows what the cache workers are currently processing.
+
+    Args:
+        limit: Maximum number of tasks to return (default 50, max 500).
+
+    Requires admin privileges.
+    """
+    return get_active_tasks(db, limit=limit)
+
+
 @router.post("/cache/retry/{package_name}")
 async def pypi_cache_retry(
     package_name: str,