🔐 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/components/MCP/CustomUserVarsSection.tsx

@@ -66,7 +66,7 @@ function AuthField({ name, config, hasValue, control, errors }: AuthFieldProps)
             placeholder={
               hasValue
                 ? localize('com_ui_mcp_update_var', { 0: config.title })
-                : localize('com_ui_mcp_enter_var', { 0: config.title })
+                : `${localize('com_ui_mcp_enter_var', { 0: config.title })} ${localize('com_ui_optional')}`
             }
             className="w-full rounded border border-border-medium bg-transparent px-2 py-1 text-text-primary placeholder:text-text-secondary focus:outline-none sm:text-sm"
           />