Fix tokenizer packaging and sequential executor handoff

[SunChJ]

Summary

• Bundle the tiktoken_ext registry in the self-contained macOS runtime.
• Make package-smoke load o200k_base, catching incomplete packages before release.
• Gracefully hand off sequential executor tasks when a terminal worker is finishing cleanup.
• Prepare downstream version 0.6.4+gloss.5 and release notes.

Validation

• uv run pytest -q tests/tools/executor/test_state.py tests/tools/executor/test_server.py — 53 passed
• Targeted release/CLI tests — 20 passed
• Ruff check and format check pass
• Fresh arm64 PyInstaller package completed dependency, layout, fake-executor, and real-executor smoke
• The 15-page Attention Is All You Need PDF completed English-to-Chinese translation with selectable text and intact visual content

Compatibility

No protocol capability or minimum Gloss version changes. Running and cancelling workers still preserve the single-active-execution boundary.