feat: Phase 2 - Orchestrator workflow node + tool-level human approval

2.1 Orchestrator in workflow:
- New run_orchestrator_node() in workflow_integration.py loads agents from DB,
  supports route/sequential/debate/pipeline modes
- New 'orchestrator' node type in workflow_engine.py execute_node dispatch

2.2 Tool-level human approval:
- AgentToolConfig extended with require_approval, approval_timeout_ms,
  approval_default fields
- New ApprovalManager (approval_manager.py) with asyncio.Event-based
  create/wait_for_decision/resolve pattern
- AgentRuntime run() and run_stream() intercept tool execution,
  wait for approval decision before executing
- New POST /api/v1/approval/{id}/resolve REST endpoint
- Frontend: approval_required SSE event handling, approval dialog UI
  with approve/deny/skip buttons

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/agent_runtime/schemas.py

@@ -12,6 +12,9 @@ class AgentToolConfig(BaseModel):
     # 若为空列表则使用全部已注册工具
     include_tools: List[str] = Field(default_factory=list, description="允许的工具名称白名单")
     exclude_tools: List[str] = Field(default_factory=list, description="排除的工具名称黑名单")
+    require_approval: List[str] = Field(default_factory=list, description="需要人工审批的工具名列表")
+    approval_timeout_ms: int = Field(default=60000, description="审批超时（毫秒），超时使用默认策略")
+    approval_default: str = Field(default="deny", description="超时默认策略: approve | deny | skip")
 
 
 class AgentMemoryConfig(BaseModel):