/install-github-app freezes interactively + /ultrareview auth errors are uninformative

Summary

Two related defects encountered while trying to use /ultrareview against
PRs in my own GitHub repo:

1. /install-github-app opens an interactive dialog that **cannot be

dismissed**: ctrl-c, esc, and enter all do nothing. I had to ctrl-z
the process and kill %1 to escape.

1. /ultrareview <PR#> fails with a single error string regardless of

which piece is misconfigured:

> Ultrareview could not start the remote session: GitHub repository
> access check failed — re-authorize GitHub in settings

The error gives no signal on which of these is missing:

• The claude GitHub App (https://github.com/apps/claude) installed on the repo
• Claude.ai-side OAuth grant (the fix in my case was /logout && /login)
• gh CLI auth
• The CLI's local OAuth store
• Repo allow-list scope inside the App install

I had to try each of them in turn to isolate the cause. /config
does not surface a GitHub integration row, so there's no "current
status" to inspect.

Repro (issue 1 — freeze)

1. Run /install-github-app in the REPL.
2. Dialog renders. No key (ctrl-c, esc, enter, q) closes it.
3. Only ctrl-z + kill %1 recovers.

Terminal: standard Linux terminal (Ubuntu 25.10, kernel 6.17.0-20-generic).
Claude Code 2.1.119.

Repro (issue 2 — opaque error)

1. Install https://github.com/apps/claude on the target repo.
2. Run /ultrareview <PR#> against a PR you own.
3. Error fires. There is no diagnostic that distinguishes "App not

installed" from "Claude.ai OAuth stale" from "wrong account" from
"repo not in App allow-list".

In my case the actual fix was /logout && /login, which I only found
after several other dead ends.

Suggested fixes

• Freeze: make ctrl-c always dismissable in /install-github-app.
• Error: have the access check report which specific precondition

failed (App install, OAuth grant, repo scope, account match), and
link to a specific remediation. A /ultrareview --doctor style
command would also help.

Environment

• Claude Code 2.1.119
• Linux 6.17.0-20-generic x86_64
• bash