* fix(worktree): track checkout PR branches correctly
Checkout-PR worktrees could point branch tracking at a PR push remote without fetching a matching remote-tracking ref. Configure same-repo PRs to track origin, make fork PR remotes fetchable before assigning upstream, and push fork PR branches to their configured remote.
* fix(worktree): scope PR push routing to Paseo targets
Review caught that using ordinary upstream config for Push could send normal branches to non-origin remotes and mishandle deduped PR branch names. Store a Paseo-specific push target during PR worktree creation, then have Push honor only that marker before falling back to origin.
* fix(worktree): use git upstream for PR pushes
* fix(worktree): allow PR checkout without head upstream
* fix(worktree): preserve fork PR git push target
* fix(worktree): preserve PR push targets
* fix(worktree): preserve PR push status
* fix(worktree): set upstream after push-only PR push
