refactor: remove knowledge base references from AI agent model and related services

- Removed KnowledgeIDs from CreateAIAgentRequest and AIAgentResponse.
- Updated buildAIAgentResponseWithLocale to eliminate knowledge base name retrieval.
- Refactored AI agent repository and service to remove knowledge base handling.
- Adjusted dashboard service to no longer track AI agents without knowledge bases.
- Modified knowledge base service to check for workflow references instead of AI agent references.
- Updated frontend components to remove knowledge base selection and display.
- Enhanced workflow validation to ensure knowledge retrieve nodes have associated knowledge bases.

web/lib/api/admin.ts

@@ -227,8 +227,6 @@ export type AIAgent = {
   fallbackMode: number
   fallbackModeName: string
   fallbackMessage: string
-  knowledgeIds: number[]
-  knowledgeBaseNames: string[]
   skillIds: number[]
   skills: { id: number; name: string }[]
   directTools: {
@@ -262,7 +260,6 @@ export type CreateAIAgentPayload = {
   handoffMode: number
   fallbackMode: number
   fallbackMessage: string
-  knowledgeIds: number[]
   skillIds: number[]
   directTools: {
     toolCode: string