migration: replace Forgejo delivery with GitHub Actions

[thedancingdeveloper]

Summary

• remove the active Woodpecker/Forgejo source, release, and container path
• add GitHub-native release binaries and website deployment workflows
• retain download-host publication using a GitHub repository secret
• remove stale Forgejo Cargo configuration and canonicalize repository/image metadata

Validation

• cargo fmt --all -- --check
• cargo check --workspace --exclude rtbit-desktop --no-default-features --features default-tls
• cargo test --workspace --exclude rtbit-desktop --no-default-features --features default-tls
• cargo clippy --workspace --exclude rtbit-desktop --no-default-features --features default-tls -- -D warnings
• ci/tasks/website-check
• ci/migration-policy.sh

The download-host key has been installed as the GitHub repository secret DEPLOY_SSH_KEY without exposing its value.