AI 写作四阶段内置智能体 Phase 1-4 落地

新增 ai-writing-researcher/outliner/writer/editor 种子 agent、_agent_runner 与 use_builtin_agents 灰度开关；四节点可按 flag 切换 SOUL 模式；时间线补大纲规划师配色并更新改造文档。

Co-authored-by: Cursor <cursoragent@cursor.com>

offline-backend-20260512/backend/app/gateway/app.py

@@ -933,6 +933,20 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
                 "Roundtable functional agent seeding failed at startup (non-fatal)"
             )
 
+        # AI 写作功能型 agent(researcher / outliner / writer / editor)缺失自动补建。
+        # 同圆桌:必须在 _sync_legacy_agents 之前,补建目录才能在同一次启动被
+        # upsert 进 agents 表,admin 启动后即可在智能体管理页编辑四个写作 agent。
+        try:
+            from app.gateway.routers._ai_writing_seed import (
+                ensure_ai_writing_functional_agents,
+            )
+
+            ensure_ai_writing_functional_agents()
+        except Exception:
+            logger.exception(
+                "AI-writing functional agent seeding failed at startup (non-fatal)"
+            )
+
         # 业务链条管理：幂等补建固定业务行（3Q/6BF/7BF/8BF），agent/chain 初始为空。
         try:
             business_mapping_store = getattr(app.state, "business_mapping_store", None)