perf(backend): 角色/世界观入库改批量——create_many 一次 flush 落全部行

角色入库端点与 toolbox world_entities 入库端点原逐卡/逐条 create（每行一次
SELECT/flush/refresh，N+1 round-trip）。新增 create_many：世界观用 add_all，
角色用一次 IN 查已有名 + 一次 flush（保持 (project_id,name) upsert 幂等与批内
重名去重、保序返回）。单条 create 薄封装 create_many，行为不变（既有调用方/E2E
复用）。复活并复用 CharacterWriteFields、新增 WorldEntityFields 作批量入参。
补两端点「多行一次落库」测试；既有幂等/冲突 gate 测试与 m5 真 pg E2E 全绿。

apps/api/ww_api/routers/toolbox.py

@@ -25,7 +25,7 @@ from ww_core.domain.outline_write_repo import OutlineWriteRepo
 from ww_core.domain.project_repo import ProjectRepo
 from ww_core.domain.repositories import MemoryRepos, OutlineRepo
 from ww_core.domain.rule_repo import RuleWriteRepo
-from ww_core.domain.world_entity_repo import WorldEntityWriteRepo
+from ww_core.domain.world_entity_repo import WorldEntityFields, WorldEntityWriteRepo
 from ww_core.orchestrator import run_generator
 from ww_db import get_session
 from ww_llm_gateway import Gateway
@@ -427,12 +427,12 @@ async def _ingest_world_entities(
             rejected_tables=rejected,
         )
 
-    created: list[str] = []
-    for entity in allowed.get("world_entities", []):
-        view = await world_write_repo.create(
-            project_id, type=entity.type, name=entity.name, rules=list(entity.rules)
-        )
-        created.append(view.name)
+    fields = [
+        WorldEntityFields(type=entity.type, name=entity.name, rules=list(entity.rules))
+        for entity in allowed.get("world_entities", [])
+    ]
+    # 批量插入（一次 flush 落全部），保序返回逐条 View。
+    created = [view.name for view in await world_write_repo.create_many(project_id, fields)]
 
     await session.commit()
     log.info(