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

dashboard/src/api/v1.ts

@@ -32,6 +32,8 @@ import {
   type DynamicConfig,
   type EnabledPatch,
   type GhproxyTestRequest,
+  type KnowledgeBaseCreateRequest,
+  type KnowledgeBaseRequest,
   type LoginRequest,
   type ListConversationsData,
   type McpServerConfig,
@@ -1366,16 +1368,16 @@ export const knowledgeApi = {
       openApiV1.getKnowledgeBase({ path: { kb_id: kbId } }),
     );
   },
-  create(config: OpenConfig) {
+  create(config: KnowledgeBaseCreateRequest) {
     return typed<OpenConfig>(
-      openApiV1.createKnowledgeBase({ body: config as any }),
+      openApiV1.createKnowledgeBase({ body: config }),
     );
   },
-  update(kbId: string, config: OpenConfig) {
+  update(kbId: string, config: KnowledgeBaseRequest) {
     return typed<OpenConfig>(
       openApiV1.updateKnowledgeBase({
         path: { kb_id: kbId },
-        body: config as any,
+        body: config,
       }),
     );
   },