PR 20023 — GitHub subdomain SSH host normalization

Before (rewritten behavior tests with production restored to main):
77 passed / 4 failed. The creation fallback also fails on the prior implementation.
After the first takeover implementation: 82 focused tests passed.
Follow-up: dotted-alias origin marked by gh-resolved lost precedence to upstream.
Before the follow-up: 82 passed / 1 failed; request incorrectly used repos/acme/web.
After the follow-up: 83 passed; request correctly uses repos/me/web at github.com.

Final focused command:
pnpm exec vp test run packages/contracts/src/pullRequest.test.ts packages/source-control-github/src/server/GitHubSourceControlProvider.test.ts packages/source-control-github/src/server/gitHubRepositoryResolution.test.ts
83 passed across 3 files.

Final integration command:
pnpm exec vp test run packages/shared/src/threadPullRequests.test.ts apps/server/src/pullRequest/PullRequestService.test.ts
247 passed across 2 files.

Targeted lint/format, scoped contracts and GitHub package typechecks, and git diff --check pass.
Original PR: 5 added test definitions across 3 files.
Final takeover: 6 added behavior definitions across 2 existing files.
Duplicate helper tests removed; distinct clone/create and marked-origin behavior retained.

Headless Linux proof uses production provider/service logic with external dependencies mocked.
No browser, credentialed live GitHub operation, macOS, Windows, iOS, Android, or Electron verification is claimed.