[W10] Release engineering and UrbanPy 0.3 publication

[Claudio9701]

Outcome

Exactly the reviewed and verified artifacts are promoted through prereleases to UrbanPy 0.3.0 and supported afterward.

Parent tasks

• build once and promote immutable sdist/wheel artifacts
• validate alpha, beta, and release candidates on TestPyPI
• publish with trusted OIDC, provenance, release notes, and versioned docs
• define rollback/yank, post-release smoke tests, and ownership
• observe security, contracts, installs, and user issues for four weeks

Acceptance

All roadmap release gates pass, no P0/P1 or unowned high risk remains, and 0.3.0 installs cleanly on the supported matrix.

Plan: PR #61