Add action pane details to user messages in chat UI

[Copilot]

This PR adds a dropdown area to user messages that shows what options were selected and their configuration when the message was sent. The implementation follows a similar UI pattern as citations in AI messages, providing users with clear visibility into which features were active.

Features Added

• Action details dropdown: Collapsible section in user messages showing selected options
• Multiple option support: Shows details for:
  • Workspace selection (scope and document name)
  • Document classification if applicable
  • Image generation status
  • Web search status
  • Prompt selection with name

Implementation Details

1. Added CSS styles for the action details container and buttons
2. Implemented a function to collect active options when sending a message
3. Created a function to generate HTML for displaying action details
4. Modified appendMessage to include action details for user messages
5. Added toggle functionality for showing/hiding action details
6. Updated backend integration to store and retrieve action details with messages

Screenshots

No screenshots provided, but the UI follows the same pattern as citations in AI messages with a gear icon (⚙️) toggle button to show/hide details.

Fixes #261.

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