feat(templates): F3b 模板库 repo + 端点（GET/POST/DELETE /templates）

- TemplateRepo/SqlTemplateRepo（list/create/delete，owner stub 过滤，只 flush 端点 commit）
- schemas/templates.py（title/body min_length=1→422）+ routers/templates.py（删不存在→404）+ main 注册
- 单测：repo CRUD/owner 隔离/frozen + 端点 201/列出/204/422×2/404

apps/api/ww_api/main.py

@@ -27,6 +27,7 @@ from ww_api.routers import (
     rules,
     settings_providers,
     style,
+    templates,
     toolbox,
 )
 from ww_api.security.credentials import _fernet
@@ -115,6 +116,7 @@ def create_app() -> FastAPI:
     app.include_router(outline.router)
     app.include_router(rules.router)
     app.include_router(style.router)
+    app.include_router(templates.router)
     app.include_router(generation.router)
     app.include_router(generation.skills_router)
     app.include_router(toolbox.router)