Related to #12325

Summary

Adds accessible labels and titles to a few obvious icon only controls in the sidebar/chat UI.This is intended as a small first pass improvement for screen reader support. It does not try to solve the full sidebar accessibility issue in one PR.

Testing

• Ran npm.cmd run lint --prefix gui
• Ran git diff --check

Notes

I kept the scope focused on controls where the action was clear from the existing UI.

Summary by cubic

Adds accessible labels and titles to sidebar/chat controls and labels the main chat input for screen readers. Addresses #12325 by clearly labeling close, send, configure, and the chat input.

• Bug Fixes
  • FindWidget: add "Close find widget" aria-label and title to the close button.
  • InputToolbar: add "Send message" aria-label and title to the submit button.
  • ModelSelect: add "Configure " to per-option cog and "Configure models" to the toolbar cog.
  • HeaderButtonWithToolTip: set aria-label and title from the text prop for icon-only header buttons.
  • TipTap editor (main input): add aria-label "Chat message input".

^{Written for commit 0b3ac42. Summary will update on new commits.}