fix: align knowledge base CRUD API contract with kb_name, canonical payload fields, and matching OpenAPI types (#9000)

Warning: Potential breaking changes in /kb related openapi.

* fix(kb): align CRUD API contract end-to-end

Unify knowledge base create/update/list with kb_name, canonical_payload,
optional list pagination with total, and matching OpenAPI plus dashboard types.

* fix: restore _model_dict references, add KnowledgeBaseCreateRequest, fix OpenAPI allOf validation

- Replace 3 remaining _model_dict() calls with payload.model_dump(exclude_none=True)
- Add KnowledgeBaseCreateRequest schema with required kb_name + embedding_provider_id
- Remove additionalProperties: false from OpenAPI allOf sub-schema to avoid validation failures
- Use Pydantic Field(alias="name") + populate_by_name=True for legacy name migration
- Delegate _canonical_kb_payload to KnowledgeBaseRequest to eliminate duplicated logic
- Add getattr default None for update_kb to prevent AttributeError
- Add validation error tests: missing kb_name, missing embedding_provider_id

* fix: address knowledge base contract follow-ups

* fix: preserve knowledge base create error shape

tests/test_fastapi_v1_dashboard.py

@@ -1192,6 +1192,34 @@ async def test_v1_openapi_uses_pydantic_request_bodies(
     assert open_api_file_upload["x-astrbot-scope"] == "file"
 
 
+@pytest.mark.asyncio
+async def test_v1_knowledge_base_create_validation_uses_api_error_shape(
+    asgi_client: httpx.AsyncClient,
+):
+    headers = _jwt_headers()
+
+    missing_name_response = await asgi_client.post(
+        "/api/v1/knowledge-bases",
+        json={"embedding_provider_id": "embedding-1"},
+        headers=headers,
+    )
+    missing_provider_response = await asgi_client.post(
+        "/api/v1/knowledge-bases",
+        json={"name": "Docs"},
+        headers=headers,
+    )
+
+    assert missing_name_response.status_code == 200
+    assert missing_name_response.json()["status"] == "error"
+    assert missing_name_response.json()["message"] == "知识库名称不能为空"
+    assert missing_provider_response.status_code == 200
+    assert missing_provider_response.json()["status"] == "error"
+    assert (
+        missing_provider_response.json()["message"]
+        == "缺少参数 embedding_provider_id"
+    )
+
+
 @pytest.mark.asyncio
 async def test_v1_conversation_path_id_allows_slash(asgi_client: httpx.AsyncClient):
     response = await asgi_client.get(