Adds /me/debug HTML page rendering the logged-in user's own session state — decoded JWT claims (no raw token, sha256[:12] fingerprint for log correlation), group memberships with sources and bound external_id when present, resource grants effective via those memberships, and a Refetch from Google (dry-run) button that diffs a fresh fetch_user_groups call against the cached user_group_members snapshot. Gated by AGNES_DEBUG_AUTH env var (default off → 404, route existence undetectable in production). Self-only by construction: user_id is read from the validated session, never echoes raw JWT / password hash / full PAT. Tolerates v13 + v14 schemas via information_schema check on users.external_id.
