Establish Gloss-maintained BabelDOC downstream

[SunChJ]

Summary

• establish this repository as the public, Gloss-maintained BabelDOC downstream, with exact upstream provenance and an explicit patch ledger
• quarantine inherited workflows that could publish to PyPI, overwrite gh-pages, or write duplicate PR feedback
• identify the first downstream release as 0.6.4+gloss.1
• add the lightweight gloss-babeldoc runtime-info --json compatibility handshake without importing the PDF/ONNX runtime
• commit the universal uv lockfile and validate lint, tests, packaging, PDF generation, and clean-wheel installation on Linux and macOS

Why

Gloss currently carries BabelDOC integration code and monkeypatches in its Swift-side Python runner. Before migrating those patches into this fork, the downstream needs a traceable upstream base, an explicit process contract, reproducible dependencies, and automation that cannot accidentally use upstream publishing channels.

This PR does not change PDF parsing, translation, typesetting, or output behavior.

Developer impact

• existing babeldoc CLI and Python imports remain available
• Gloss can discover compatibility through capabilities and runtime_api_version instead of an exact upstream package-version check
• downstream releases will use GitHub Releases or a Gloss-managed manifest, not the upstream public PyPI project
• future upstream synchronization is performed one reviewed release tag at a time, preserving ancestry with merge commits

Validation

• uv lock --check
• uv run ruff check .
• uv run pytest -q — 5 passed
• uv build --wheel --sdist
• clean Python 3.12 wheel installation and runtime-handshake validation
• no-secret PDF E2E on macOS arm64 — completed successfully in 10.51 seconds
• GitHub workflow YAML parsed successfully; all remaining actions are pinned to full commit SHAs

Follow-up

Move the existing Gloss Python runner and monkeypatches into this repository in focused PRs, beginning with service lifecycle and structured progress. Font, save, and IL-cache performance changes remain out of this foundation PR.