fix(verify-and-ship): pin PR target to origin so forks don't hit upstream

[TropicalDog17]

Problem

gh pr create defaults a fork's PR to the upstream parent repo. Because origin here is a fork of cyrusagents/cyrus, sessions running the verify-and-ship skill silently opened PRs on the public upstream instead of the fork — e.g. cyrusagents#1376 (closed, reopened as fork #49) and cyrusagents#1369 (closed; the work had already merged as fork #29).

Fix

The GitHub PR step now derives the target from origin and passes it explicitly, so the PR always lands on the fork:

PR_REPO="$(gh repo view --json nameWithOwner -q .nameWithOwner)"
PR_HEAD="$(git branch --show-current)"
gh pr create --repo "$PR_REPO" --head "$PR_HEAD" --draft --base <base_branch> ...

Also adds a load-bearing note explaining the fork default and the "4-digit PR number = wrong repo" red flag.

Docs-only change to skills/verify-and-ship/SKILL.md.

https://claude.ai/code/session_01Y7j2xZhmHbNhMRq6665PXy