fix(db): 种子智能体彻底幂等 — INSERT OR IGNORE(复合唯一) + port 默认 ''

-add_agent 改用 SQLite on_conflict_do_nothing((id,user_id,port))，杜绝运行时/重跑 UNIQUE；
port 无端口身份默认 ''（agents.port NOT NULL）。真实库 migrate+seed 连续 3 次均成功。

app/infrastructure/seed.py

@@ -256,17 +256,16 @@ DEMO_USERS = [
 
 
 async def _add_agent(session: AsyncSession, seed: dict, user_id: str, port: str | None, now: str) -> None:
-    """幂等播种单个智能体：按 (id,user_id,port) 已存在则跳过（修全局固定 id 多用户/端口填重）。"""
-    key = (seed["id"], user_id, port)
-    if await session.get(Agent, key) is not None:
-        return
-    session.add(
-        Agent(id=seed["id"], user_id=user_id, port=port, name=seed["name"],
-              description=seed["description"], language=seed.get("language", "zh"),
-              model_name=seed.get("model_name", ""), deletable=seed.get("deletable", True),
-              use_fixed_soul=seed.get("use_fixed_soul", False),
-              created_at=now, updated_at=now)
-    )
+    """幂等播种单个智能体：SQLite INSERT OR IGNORE（(id,user_id,port) 冲突跳过），杜绝 UNIQUE 抛错。"""
+    from sqlalchemy.dialects.sqlite import insert as sqlite_insert
+    port_val = port or ""   # agents.port NOT NULL；无端口身份用 ""
+    stmt = sqlite_insert(Agent).values(
+        id=seed["id"], user_id=user_id, port=port_val, name=seed["name"],
+        description=seed["description"], language=seed.get("language", "zh"),
+        model_name=seed.get("model_name", ""), deletable=seed.get("deletable", True),
+        use_fixed_soul=seed.get("use_fixed_soul", False), created_at=now, updated_at=now,
+    ).on_conflict_do_nothing(index_elements=["id", "user_id", "port"])
+    await session.execute(stmt)
 
 
 async def seed_data(session: AsyncSession) -> None: