fix(git-tools): pr-merge queue guard reads CI status from the BASE repo (fork PRs, B1)

For a fork PR, pr-metadata's headRepository names the fork (e.g.
stack-mos-dt-0/stack), and pr-merge passed it to ci-queue-wait via -R.
Woodpecker posts commit statuses on the BASE repository, so the guard read
statuses:null from the fork and every fork merge aborted with
state=malformed rc=3 (#1215, gate-merge-01 B1; standalone queue-wait
against the base repo returns terminal-success on the same sha). Same
family as d339e8fd.

- pr-metadata.sh: normalize baseRepository from Gitea base.repo.full_name
- pr-merge.sh: pass the BASE repo to the queue guard; head repo remains
  for head-sha identity; origin-repo fallback when metadata carries no
  base repository (correct for same-repo PRs)
- test-pr-merge-fork-ci-status.sh: fork-PR regression, CI-reachable via
  test:framework-shell beside its siblings; asserts the guard NEVER sees
  the fork and gets the base repo, head branch and exact sha
- test-pr-merge-queue-branch.sh: its old -R assertion pinned the fork
  repo, i.e. the bug; now asserts the base repo

packages/mosaic/framework/tools/git/pr-metadata.sh

@@ -209,6 +209,10 @@ base_ref = first_non_empty(
     data.get('base_ref'),
     data.get('base_label'),
 )
+base_repo = first_non_empty(
+    nested(data, 'base', 'repo', 'full_name'),
+    nested(data, 'base', 'repo', 'name_with_owner'),
+)
 
 if not head_ref or not base_ref:
     available = ', '.join(sorted(data.keys()))
@@ -229,6 +233,7 @@ normalized = {
     'headRefOid': head_sha,
     'headRepository': head_repo,
     'baseRefName': base_ref,
+    'baseRepository': base_repo,
     'labels': [l.get('name', '') for l in data.get('labels', []) if isinstance(l, dict)],
     'assignees': [a.get('login', '') for a in data.get('assignees', []) if isinstance(a, dict)],
     'milestone': nested(data, 'milestone', 'title') or '',