feat: Auto-retry tasks, 403 proxy rotation, task deletion

- Fix 403 handler to rotate BOTH proxy and fingerprint (was only fingerprint)
- Add auto-retry logic to task service (retry up to max_retries before failing)
- Add error tooltip on task status badge showing retry count and error message
- Add DELETE /api/tasks/:id endpoint (only for non-running tasks)
- Add delete button to JobQueue task table

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/routes/tasks.ts

@@ -145,6 +145,36 @@ router.get('/:id', async (req: Request, res: Response) => {
   }
 });
 
+/**
+ * DELETE /api/tasks/:id
+ * Delete a specific task by ID
+ * Only allows deletion of failed, completed, or pending tasks (not running)
+ */
+router.delete('/:id', async (req: Request, res: Response) => {
+  try {
+    const taskId = parseInt(req.params.id, 10);
+
+    // First check if task exists and its status
+    const task = await taskService.getTask(taskId);
+    if (!task) {
+      return res.status(404).json({ error: 'Task not found' });
+    }
+
+    // Don't allow deleting running tasks
+    if (task.status === 'running' || task.status === 'claimed') {
+      return res.status(400).json({ error: 'Cannot delete a running or claimed task' });
+    }
+
+    // Delete the task
+    await pool.query('DELETE FROM worker_tasks WHERE id = $1', [taskId]);
+
+    res.json({ success: true, message: `Task ${taskId} deleted` });
+  } catch (error: unknown) {
+    console.error('Error deleting task:', error);
+    res.status(500).json({ error: 'Failed to delete task' });
+  }
+});
+
 /**
  * POST /api/tasks
  * Create a new task