refactor: consolidate agent marketplace endpoints into main agents API and improve data management consistency

- Remove dedicated marketplace controller and routes, merging functionality into main agents v1 API
  - Add countPromotedAgents function to Agent model for promoted agents count
  - Enhance getListAgents handler with marketplace filtering (category, search, promoted status)
  - Move getAgentCategories from marketplace to v1 controller with same functionality
  - Update agent mutations to invalidate marketplace queries and handle multiple permission levels
  - Improve cache management by updating all agent query variants (VIEW/EDIT permissions)
  - Consolidate agent data access patterns for better maintainability and consistency
  - Remove duplicate marketplace route definitions and middleware

api/server/routes/agents/v1.js

@@ -42,6 +42,11 @@ router.use('/actions', actions);
  */
 router.use('/tools', tools);
 
+/**
+ * Get all agent categories with counts
+ * @route GET /agents/marketplace/categories
+ */
+router.get('/categories', v1.getAgentCategories);
 /**
  * Creates an agent.
  * @route POST /agents