codeArbiter 2.5.1: macOS/Windows scope-reminder fix + release-skill ca-scoping

Fixed

• Scope-touch reminders now fire on macOS and Windows (H-12/H-15/H-16/H-13).
  post-write-edit.py derived its repo-relative path with a lexical os.path.relpath. When
  the hook payload's file_path and git rev-parse --show-toplevel named the same repo via
  divergent forms (a symlinked /var vs /private/var on macOS, an 8.3 short name on
  Windows), the path came out ..-prefixed and every path-scoped reminder was silently
  dropped. A new _hooklib.repo_rel() canonicalizes both sides with realpath first. (#125)
• /ca:release is now scoped to the ca plugin (ADR-0007). The skill assumed a
  single-plugin repo: LAST_TAG resolved via bare git describe (returning a ca-sandbox
  tag), the bump and commit window spanned the whole repo, the derived version was never
  asserted against plugin.json, and the README/catalog surfaces had no sync step. All are
  now scoped to plugins/ca/ and enforced, including a read-back of the published Release. (#125)