fix(chat): restore focus to chat input after closing keyboard shortcuts modal

[kareena0229]

Related Issue

Closes #821

Summary

This PR improves keyboard accessibility by automatically restoring focus to the chat input after the Keyboard Shortcuts help modal is closed.

Users can now continue typing immediately without needing to manually click the input field.

Changes Made

• Added a reusable closeHelpModal helper.
• Restores focus to the chat input using textareaRef.current?.focus().
• Preserves focus restoration regardless of how the modal is dismissed:

1. Close button (×)
2. Clicking outside the modal
3. Pressing Esc

• Keeps existing modal behavior unchanged.

Why This Change?

Previously, closing the Keyboard Shortcuts modal left keyboard focus undefined, requiring keyboard users to manually click the chat input before continuing.

This update provides a smoother and more accessible keyboard workflow while following common focus management practices.

Testing

• ✅ Modal closes via close button and focus returns to the chat input.

• ✅ Modal closes by clicking outside and focus returns to the chat input.

• ✅ Modal closes using the Esc key and focus returns to the chat input.

• ✅ Existing chat functionality remains unaffected.

• ✅ npm run build passes.

• ✅ npm run lint completes with no errors related to this change.

• ☑️ I have tested my changes locally.

• ☑️ My code follows the project's coding style.

• ☑️ This PR addresses issue [Enhancement] Restore Keyboard Focus to Chat Input After Closing Keyboard Shortcuts Modal #821.

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