fix(release): restore private style marker boundary

[moonweave]

Summary

• restore the established split-marker contract for the internal target format in themes/journal_export_policy.py
• keep internal_style_format runtime behavior unchanged while preventing the private marker from entering public source/package scans
• add a regression test for the export-policy boundary
• regenerate docs/packaging/public-release-status.md

Root cause

The export-policy extraction introduced a contiguous private style marker even though the rest of the style compatibility surface already constructs the marker from split fragments. The conservative public-release scanner therefore blocked an otherwise approved candidate.

This patch does not rename, remove, or weaken the internal style behavior. It restores the existing release-boundary convention used by hub_core/config_style.py, themes/journal_theme.py, and themes/style_profiles.py.

Validation

• focused release/style tests: 51 passed
• python scripts/check_public_release.py: passed
• public inventory: repository technical gate ok, zero blockers
• wheel build: figops-0.20.2-py3-none-any.whl
• public package surface inspection: passed, 479 members, zero blockers
• guarded TestPyPI dry-run: passed
• Ruff and git diff --check: passed

The local isolated installed-surface smoke remains environment-limited by missing cycler; the existing GitHub CI gate is required before merge.