fix: make the label say the email, rather, than name (#62)

[andrinoff]

This pull request makes a minor update to the way account tabs are labeled in the inbox UI. Now, the tab label always uses the account's email address, even if a display name is present.

• Always use the account email as the label for each tab in the inbox, removing previous logic that preferred the account's display name if available (tui/inbox.go).

Before:

After: