The terminal shows a repository's upstream, checks it now, and lets an admin turn following on or off #3559

For: the same action has the same shape on the page and in the terminal (split from #3442).

Done:

• [ ] src/tui/screens/about.ts shows an 'upstream' row with the URL, branch and last check, under the page's rule: shown when following is on, or to an admin when it is off.
• [ ] A writer-gated key runs 'Check upstream now' through the same action the page uses, and shows its answer.
• [ ] An admin-only key turns following on or off through setFollowUpstream, the way the screen already edits settings through updateRepoSettings.
• [ ] A test drives the screen: a reader sees no keys, a writer checks, an admin toggles.

Files: src/tui/screens/about.ts, a test under test/tui-*. Risk: none beyond the gating; reuse the page's permission checks.