Pull requests: row text leftovers (gap before Layer, phone lead truncation, Azure 'updated' is the creation date) #717

Three small text problems on PR rows and pages:

• desktop rows: after a truncated branch pair ("→…") there is a wider gap before "· Layer" because the branches box keeps max_w(50%) and its truncated text does not fill it (crates/ui/src/pull_requests/mod.rs);
• phone rows: the lead "source · author · branches" truncates from its end, producing "Created fr.." with an extra space after the ellipsis; the author should give way first as on desktop;
• Azure DevOps PRs show "updated 156d ago" that is really the creation date, because Azure has no last-updated time (snapshot updated_at = closedDate else creationDate); the label should say "created" when the host has no update time, or the field should be optional.
  Found by the fix(ui): phone pull request surfaces #689 and feat: Azure DevOps pull requests #702 reviews.