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/assets/link-gray.svg

@@ -1,3 +1,3 @@
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