FEATURE: add support for uploads when starting a convo

[SamSaffron]

This commit introduces file upload capabilities to the AI Bot conversations interface and improves the overall dedicated UX experience. It also changes the experimental setting to a more permanent one.

Key changes:

• File upload support:

  • Integrates UppyUpload for handling file uploads in conversations
  • Adds UI for uploading, displaying, and managing attachments
  • Supports drag & drop, clipboard paste, and manual file selection
  • Shows upload progress indicators for in-progress uploads
  • Appends uploaded file markdown to message content

• Renamed setting:

  • Changed ai_enable_experimental_bot_ux to ai_bot_enable_dedicated_ux
  • Updated setting description to be clearer
  • Changed default value to true as this is now a stable feature
  • Added migration to handle the setting name change in database

• UI improvements:

  • Enhanced input area with better focus states
  • Improved layout and styling for conversations page
  • Added visual feedback for upload states
  • Better error handling for uploads in progress

• Code organization:

  • Refactored message submission logic to handle attachments
  • Updated DOM element IDs for consistency
  • Fixed focus management after submission

• Added tests:

  • Tests for file upload functionality
  • Tests for removing uploads before submission
  • Updated existing tests to work with the renamed setting

[keegangeorge]

Two small suggestions to use existing functions, otherwise, LGTM!