a11y: add aria-label to response action buttons for screen readers

[adityasingh2400]

Summary

Fixes #12326 (problem 1 only — chat response action buttons).

The Insert / Copy / Apply / Diff / Compact / Generate-rule / Continue / Delete / Helpful / Unhelpful buttons in chat responses are pure-icon elements with a hover tooltip but no accessible name. NVDA and other screen readers announce them as just "button" or "unlabeled button," which is the specific blocker called out in the issue.

This PR adds an aria-label to each toolbar button, matching the user-visible action. Pure prop additions, no behavior or styling changes.

Changes

• gui/src/components/gui/HeaderButtonWithToolTip.tsx — accept an optional aria-label prop and default it to the existing tooltip text so every consumer (FeedbackButtons, CopyIconButton, ResponseActions, History rows, etc.) gains an accessible name automatically.
• gui/src/components/StyledMarkdownPreview/StepContainerPreToolbar/*.tsx — add aria-label (and role="button" for div-based clickables) to:
  • InsertButton -> "Insert at cursor"
  • CopyButton -> "Copy code block" / "Code copied"
  • ApplyActions Apply -> "Apply changes"
  • ApplyActions Accept / Reject (via ToolbarButtonWithTooltip) -> "Accept all diffs" / "Reject all diffs"
  • CreateFileButton -> "Create file with code"
  • RunInTerminalButton -> "Run command in terminal"

The broader sidebar / settings / model-selector accessibility audit described in #12325 is out of scope for this first cut; this is the buttons-only piece called out in #12326.

Test plan

• Build the GUI and confirm chat response action buttons announce their action name in NVDA / VoiceOver / Narrator.
• Hover tooltips still appear unchanged.
• Visual layout of the action toolbar is unchanged.
• No regressions in existing keyboard / click behavior.

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Summary by cubic

Add aria-labels to chat response action buttons so screen readers announce clear names. Fixes #12326 for buttons only with no visual or behavior changes.

• Bug Fixes
  • Labeled buttons: Insert, Copy (incl. “Code copied”), Apply, Accept all diffs, Reject all diffs, Create file, Run in terminal.
  • HeaderButtonWithToolTip and ToolbarButtonWithTooltip accept aria-label and default to the tooltip; added role="button" for div-based clickables.
  • Matches the button-accessibility requirement in Continue extension is completely inaccessible with NVDA screen reader — unlabeled buttons and inaccessible settings #12326; tooltips and layout remain unchanged.

^{Written for commit f05e209. Summary will update on new commits. Review in cubic}

[github-actions]

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[cubic-dev-ai]

No issues found across 7 files

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[adityasingh2400]

I have read the CLA Document and I hereby sign the CLA