Add safe human handoff for source workflows

[Pigbibi]

Summary

• Source workflows now use read-only contents: read permissions.
• Generated output is emitted as a binary-safe patch plus HUMAN_REQUIRED receipt; artifacts upload with always().
• The workflow no longer auto-creates a PR, merges, or deploys.

Fresh verification

• uv run --locked --extra test python -m pytest -q — 134 passed
• Ruff on modified Python files, actionlint on modified workflows, compileall, and git diff --check
• Temporary Git probe: text/binary patch applies; receipt bytes are stable; handoff path invokes no remote command.