[Feature]: Add Azure DevOps PR thread setup for same-repo pull request URLs

[Joehoel]

Problem or use case

The current "Checkout Pull Request" flow is GitHub-specific. The web UI only accepts GitHub PR references, and the server resolves/prepares PR threads through GitHub-specific handling.

For a local repo hosted on Azure DevOps, that means existing pull requests cannot be used as the entrypoint for a new thread, even when the repo is otherwise a normal Git checkout.

Proposed solution

Add a narrow first pass for Azure DevOps-hosted repos:

• detect common same-repo Azure DevOps remotes
• accept Azure DevOps pull request URLs in the PR checkout flow
• resolve PR metadata for those URLs
• prepare a draft thread from that PR in local or worktree mode

Keep the current GitHub flow unchanged.

Why this matters

This would let Azure DevOps users reuse the existing PR-based thread workflow instead of manually checking out branches outside t3code.

Smallest useful scope

Support existing same-repo Azure DevOps PR URLs for:

• resolvePullRequest
• preparePullRequestThread
• web input parsing and dialog copy

Out of scope for this first pass:

• Azure DevOps PR creation
• fork PR support
• number-only PR references without a URL

Alternatives considered

Manual branch checkout works, but it bypasses the existing PR entrypoint and loses the "paste PR URL and start from there" workflow.

Risks or tradeoffs

Azure DevOps remote and PR URL formats vary across HTTPS and SSH forms, so the first pass should stay limited to common same-repo formats.

Contribution

I plan to implement this if the scope looks acceptable.