Terminal: open the private repository a writer fixes a sealed report in #6464

The page (src/web/pages/issues.ts, privateRepoForSealed), the API (POST …/issues/:number/private) and now MCP (seal with action: "private", #4993) all give a writer the private repository to fix a sealed report in. The terminal has no way to do this. Add a key on a sealed issue's screen in src/tui that calls privateRepoForSealed and shows the repo name and clone URL (built from the forge's origin), with the same refusals: not_found for anyone who may not see the issue, not_sealed, and unverified. Add a test that drives it, and a line in the README.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.