ci(release): one-time self-hosted PyPI recovery for v4.20.0

[AetherAI3]

Purpose

Permit a one-time v4.20.0 PyPI publication from the reviewed self-hosted Linux pool while GitHub-hosted Actions and artifact storage are unavailable. The owner explicitly approved the manual release exception.

Guardrails

• Opt-in manual_self_hosted input defaults to false; release-published events keep the hosted route.
• Only a dispatch from main with the exact v4.20.0 tag passes the recovery guard.
• The pypi-production environment still requires owner review, and the existing PyPI trusted publisher receives a short-lived GitHub OIDC identity.
• Version agreement, tests, type checks, wheel/sdist build, and wheel smoke test remain required.
• Artifact upload is attempted and its failure is visible, but the approved exception lets the publish continue; SHA-256 digests and source commit are printed in logs.

The normal protected workflow remains unchanged by default. Remove this one-time option after the release.