🔐 refactor: Improve MCP Auth UX for Agent Panel (#9762)

* chore: Improve logging format for initial flow state creation

* refactor: MCP Tool Management with Improved Auth Handling and State Management

- Updated `CustomUserVarsSection` to include optional localization for placeholder text.
- Refactored `MCPToolSelectDialog` to streamline tool addition and management, including improved handling of authentication data.
- Introduced a new `addToolsToForm` function to encapsulate logic for adding tools to the form state.
- Enhanced `useRemoveMCPTool` hook to simplify tool removal logic and ensure proper state updates.
- Added loading state management for custom variable saving to improve user experience.

* refactor: Enhance MCP Tool Removal Logic and Integrate Toast Notifications

- Updated `MCPToolSelectDialog` to utilize the new `removeTool` function from the `useRemoveMCPTool` hook for improved tool removal handling.
- Refactored `useRemoveMCPTool` to accept options for toast notifications, allowing for more flexible user feedback during tool removal.
- Removed the previous inline tool removal logic to streamline the component's code and improve maintainability.

* refactor: Enhance user plugins mutation to invalidate MCP auth values on uninstall

* refactor: Replace refetchQueries with invalidateQueries for improved cache management

* chore: remove unused i18n key

client/src/locales/en/translation.json

@@ -834,7 +834,6 @@
   "com_ui_delete_success": "Successfully deleted",
   "com_ui_delete_tool": "Delete Tool",
   "com_ui_delete_tool_confirm": "Are you sure you want to delete this tool?",
-  "com_ui_delete_tool_error": "Error while deleting the tool: {{error}}",
   "com_ui_delete_tool_save_reminder": "Tool removed. Save the agent to apply changes.",
   "com_ui_deleted": "Deleted",
   "com_ui_deleting_file": "Deleting file...",