Resolves the case where a remote like `git@github-work:owner/repo.git`
points at github.com via `~/.ssh/config` but Paseo treats it as
non-GitHub.
Adds a centralized GitHub remote resolver that parses standard remotes
directly and resolves SSH aliases via `ssh -G` (with hostname
validation to keep the alias out of ssh's option parser). The resolver
is shared by workspace GitHub feature detection, PR status, PR
creation, and workspace git metadata.
