feat(frontend): add stop button to cancel streaming response

[bot-kiwi]

Summary

Add a Stop button to cancel streaming AI responses. When the assistant is generating a response, users can now click the Stop button (replacing the Send button) to abort the stream instead of waiting for it to complete. The partial message remains in place after stopping.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation update
• CI/CD or infrastructure change

Changes Made

• Added stop to the useChat destructuring in ProjectChat.tsx
• Replaced Send button with Stop button (Square icon) when isAssistantTyping is true
• Added stop.response i18n key in both de.json and en.json with appropriate translations
• Stop button uses aria-label via the i18n string for accessibility

Related Issues

Closes #484

Supersedes PR #485 (closed without merging).

Testing

• I have tested these changes locally
• I have added/updated tests as appropriate
• All existing tests pass

Checklist

• My code follows the project's coding standards
• I have updated documentation as needed
• I have run make generate if SQL queries were modified (backend)
• I have updated barrel exports if components were added (frontend)

Screenshots (if applicable)

[greptile-apps]

Greptile Summary

This PR adds a Stop button to cancel in-flight streaming AI responses, swapping the Send button for a Square icon button while isAssistantTyping is true. The change is minimal and well-scoped.

• stop is destructured from useChat and called on click; isAssistantTyping is correctly removed from the Send button's disabled check in the else branch since the button is only rendered when the condition is already false.
• The new stop.response i18n key is added to both en.json and de.json, matching the placement and naming pattern of neighboring keys like stop.recording.

Confidence Score: 5/5

Safe to merge — the change is a small, self-contained UI toggle that adds a Stop button when the assistant is streaming and restores the Send button otherwise.

All three modified files have clean, focused changes: the component correctly conditions on isAssistantTyping, removes the now-redundant guard from the Send button's disabled list, and the i18n additions are consistent with neighboring keys. No logic paths or state transitions appear broken.

No files require special attention.

Important Files Changed

Filename	Overview
apps/frontend/components/chat/ProjectChat.tsx	Destructures stop from useChat and replaces the Send button with a Stop button (Square icon) when isAssistantTyping is true; the isAssistantTyping guard is correctly removed from the Send button's disabled check in the else branch.
apps/frontend/messages/en.json	Adds stop.response i18n key with value "Stop response".
apps/frontend/messages/de.json	Adds stop.response i18n key with German translation "Antwort stoppen".

_{Reviews (1): Last reviewed commit: "fix(frontend): add missing stop.response..." | Re-trigger Greptile}