[tmm]

More zbugs-gpui parity with the web app:

• Multi-line comments: the comment field is a textarea that grows from 2 to 10 rows. Return adds a line, and ⌘Enter (Ctrl+Enter elsewhere) posts it, as the web app's comment composer. ⌘Enter also saves the New issue, Edit issue, and Edit comment dialogs. It's one binding, Confirm { secondary: true } in text fields, which the comment box and gpui-kit's dialogs handle.
• Toasts: when someone else comments on or reacts to the issue you're looking at, a notification says so ("arv posted a new comment", "tantaman reacted on this issue: 🎉"), as the web app's toasts. Your own comments and reactions don't toast, and nothing toasts until the server has confirmed the issue.

The macOS e2e now posts its first comment by pressing ⌘Enter in the comment field. I checked the toasts by hand, inserting another user's comment and reaction in Postgres while the issue was open.