main:新增并发控制功能

变更内容：
- 增加 `max_concurrent_jobs` 配置项，支持设置最大并发任务数。
- 为 `JobManager` 添加信号量控制实现任务并发限制。
- 新增获取任务并发状态的接口 `/jobs/concurrency/status`。
- 编写并发控制功能相关的测试用

tests/test_job_manager.py

@@ -186,6 +186,10 @@ class TestJobManagerWithMocks:
         manager._redis_client = mock_redis
         manager._register_algorithms()
 
+        # 初始化 semaphore
+        import asyncio
+        manager._semaphore = asyncio.Semaphore(10)
+
         await manager.execute_job("test-job-id")
 
         # 验证状态更新被调用
@@ -399,3 +403,97 @@ class TestWebhook:
 
         # 验证重试次数
         assert mock_http.post.call_count == 2
+
+
+class TestConcurrencyControl:
+    """测试并发控制功能"""
+
+    @pytest.mark.asyncio
+    async def test_get_concurrency_status(self):
+        """测试获取并发状态"""
+        manager = JobManager()
+
+        # 初始化 semaphore
+        manager._max_concurrent_jobs = 10
+        manager._semaphore = asyncio.Semaphore(10)
+
+        status = manager.get_concurrency_status()
+
+        assert status["max_concurrent"] == 10
+        assert status["available_slots"] == 10
+        assert status["running_jobs"] == 0
+
+    @pytest.mark.asyncio
+    async def test_get_concurrency_status_without_semaphore(self):
+        """测试未初始化 semaphore 时获取并发状态"""
+        manager = JobManager()
+
+        status = manager.get_concurrency_status()
+
+        assert status["max_concurrent"] == 0
+        assert status["available_slots"] == 0
+        assert status["running_jobs"] == 0
+
+    @pytest.mark.asyncio
+    async def test_concurrency_limit(self):
+        """测试并发限制是否生效"""
+        manager = JobManager()
+
+        # 设置较小的并发限制
+        manager._max_concurrent_jobs = 2
+        manager._semaphore = asyncio.Semaphore(2)
+
+        # 模拟 Redis
+        mock_redis = AsyncMock()
+        mock_redis.hgetall = AsyncMock(
+            return_value={
+                "status": "pending",
+                "algorithm": "PrimeChecker",
+                "params": '{"number": 17}',
+                "webhook": "",
+                "request_id": "test-request-id",
+                "created_at": "2026-02-02T10:00:00+00:00",
+            }
+        )
+        mock_redis.hset = AsyncMock()
+        mock_redis.expire = AsyncMock()
+        manager._redis_client = mock_redis
+        manager._register_algorithms()
+
+        # 创建一个慢速任务
+        async def slow_execute():
+            async with manager._semaphore:
+                await asyncio.sleep(0.1)
+
+        # 启动 3 个任务
+        tasks = [asyncio.create_task(slow_execute()) for _ in range(3)]
+
+        # 等待一小段时间，让前两个任务获取 semaphore
+        await asyncio.sleep(0.01)
+
+        # 检查并发状态
+        status = manager.get_concurrency_status()
+        assert status["running_jobs"] == 2  # 只有 2 个任务在运行
+        assert status["available_slots"] == 0  # 没有可用槽位
+
+        # 等待所有任务完成
+        await asyncio.gather(*tasks)
+
+        # 检查最终状态
+        status = manager.get_concurrency_status()
+        assert status["running_jobs"] == 0
+        assert status["available_slots"] == 2
+
+    def test_concurrency_status_api(self, client):
+        """测试并发状态 API 端点"""
+        response = client.get("/jobs/concurrency/status")
+
+        assert response.status_code == status.HTTP_200_OK
+        data = response.json()
+
+        assert "max_concurrent" in data
+        assert "available_slots" in data
+        assert "running_jobs" in data
+        assert isinstance(data["max_concurrent"], int)
+        assert isinstance(data["available_slots"], int)
+        assert isinstance(data["running_jobs"], int)