feat: 标签管理功能 + 问答前缀对用户隐藏

标签管理:
- 新增 tags/tag_assignments 持久化层、迁移、/api/tags 路由
- 标签分智能体/技能/定时任务三类, 仅同类型可互打, 仅 admin 可增删改与打标签
- 三类资源列表支持按名称模糊检索与按标签筛选(走后端查询参数)
- 前端新增标签管理页、TagPickerDialog(点击即时绑定)、彩色标签 chip

问答前缀:
- 前缀不再拼入消息 content, 改存 additional_kwargs 由 PromptPrefixMiddleware
  在调模型前临时注入, 用户界面看不到前缀但模型仍收到
- 修正 thread_existed 闸门导致首轮前缀被跳过的问题

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

offline-backend-20260512/backend/packages/harness/deerflow/agents/lead_agent/agent.py

@@ -8,9 +8,10 @@ from deerflow.agents.lead_agent.prompt import apply_prompt_template
 from deerflow.agents.memory.summarization_hook import memory_flush_hook
 from deerflow.agents.middlewares.clarification_middleware import ClarificationMiddleware
 from deerflow.agents.middlewares.loop_detection_middleware import LoopDetectionMiddleware
-from deerflow.agents.middlewares.memory_middleware import MemoryMiddleware
-from deerflow.agents.middlewares.setup_agent_approval_middleware import SetupAgentApprovalMiddleware
-from deerflow.agents.middlewares.subagent_limit_middleware import SubagentLimitMiddleware
+from deerflow.agents.middlewares.memory_middleware import MemoryMiddleware
+from deerflow.agents.middlewares.prompt_prefix_middleware import PromptPrefixMiddleware
+from deerflow.agents.middlewares.setup_agent_approval_middleware import SetupAgentApprovalMiddleware
+from deerflow.agents.middlewares.subagent_limit_middleware import SubagentLimitMiddleware
 from deerflow.agents.middlewares.summarization_middleware import BeforeSummarizationHook, DeerFlowSummarizationMiddleware
 from deerflow.agents.middlewares.title_middleware import TitleMiddleware
 from deerflow.agents.middlewares.todo_middleware import TodoMiddleware
@@ -257,6 +258,10 @@ def _build_middlewares(
     resolved_app_config = app_config or get_app_config()
     middlewares = build_lead_runtime_middlewares(app_config=resolved_app_config, lazy_init=True)
 
+    # Inject the admin prompt prefix into the model request (kept out of the
+    # persisted/displayed message so the user never sees it).
+    middlewares.append(PromptPrefixMiddleware())
+
     # Add summarization middleware if enabled
     summarization_middleware = _create_summarization_middleware(app_config=resolved_app_config)
     if summarization_middleware is not None:
@@ -304,10 +309,10 @@ def _build_middlewares(
     if custom_middlewares:
         middlewares.extend(custom_middlewares)
 
-    middlewares.append(SetupAgentApprovalMiddleware())
-
-    # ClarificationMiddleware should always be last
-    middlewares.append(ClarificationMiddleware())
+    middlewares.append(SetupAgentApprovalMiddleware())
+
+    # ClarificationMiddleware should always be last
+    middlewares.append(ClarificationMiddleware())
     return middlewares