fix(popup): map edited timestamp to threaded-annotations updatedAt

[jackiejou]

Summary

The threaded-annotations v2 thread component shows an edited indicator on a message when its updatedAt is set to a timestamp newer than createdAt. The box-annotations adapter was not populating updatedAt, so even after the user edited an annotation in PopupV2, the thread never rendered the indicator.

This change maps Annotation.modified_at to the root message updatedAt when it differs from created_at. Replies are unaffected because the API model has no modified_at on Reply and the adapter forces canEdit: false for replies.

Implementation notes

• Compares parsed instants (getTime()) rather than raw ISO strings, so equivalent normalizations (Z vs +00:00, fractional precision) are treated as unedited.
• Falls back to undefined for unparseable modified_at. The consumer simply hides the indicator in that case rather than crashing the popup; the field is optional in the public type.

Test plan

• Open an annotation in the threaded popup, edit the root message, save, and confirm the edited indicator renders
• Reload the file with the edited annotation already on disk and confirm the indicator still renders on the root message
• Confirm an unedited annotation does not render the indicator
• Confirm replies do not render the indicator (they have no editable timestamp in the model)