test(knowledge): 颜色校验走 422，修正过长行

backend/tests/test_knowledge_categories.py

@@ -342,7 +342,9 @@ async def test_category_color_roundtrip(client: AsyncClient) -> None:
     base = f"{V1}/workspaces/{ws_id}/knowledge/categories"
 
     created = unwrap(
-        await client.post(json={"name": "部署", "color": "#4f46e5"}, url=base, headers=user["headers"])
+        await client.post(
+            url=base, json={"name": "部署", "color": "#4f46e5"}, headers=user["headers"]
+        )
     )
     # 统一成大写，前端不用再 casefold
     assert created["color"] == "#4F46E5"
@@ -387,14 +389,16 @@ async def test_category_color_roundtrip(client: AsyncClient) -> None:
     assert renamed["name"] == "上线"
     assert renamed["color"] == "#10B981"
 
-    bad = await client.post(json={"name": "业务", "color": "red"}, url=base, headers=user["headers"])
-    assert bad.status_code == 400, bad.text
+    bad = await client.post(
+        url=base, json={"name": "业务", "color": "red"}, headers=user["headers"]
+    )
+    assert bad.status_code == 422, bad.text
     assert _code(bad) == 1002
 
     too_long = await client.post(
         json={"name": "业务2", "color": "#4f46e5cc"}, url=base, headers=user["headers"]
     )
-    assert too_long.status_code == 400, too_long.text
+    assert too_long.status_code == 422, too_long.text
 
 
 @pytest.mark.asyncio