feat: enhance agent sharing functionality and UI improvements

- Added shared agents state management in Navigation and AgentsList components.
- Implemented fetching and displaying shared agents in the AgentsList.
- Introduced functionality to hide shared agents with appropriate API integration.
- Updated the SharedAgent component layout for better UI consistency.
- Improved error handling in conversation fetching logic.
- Added new API endpoint for hiding shared agents.
- Updated Redux slice to manage shared agents state.
- Refactored AgentCard and AgentSection components for better code organization and readability.

frontend/src/store.ts

@@ -42,6 +42,7 @@ const preloadedState: { preference: Preference } = {
     modalState: 'INACTIVE',
     paginatedDocuments: null,
     agents: null,
+    sharedAgents: null,
     selectedAgent: null,
   },
 };