Prepare the v0.9.0 release - #73

Release

Finalizes miniVERL v0.9.0 after the green product merge fb78f64.

• sets the canonical release state, package version and citation to 0.9.0
• freezes the v0.9.0 changelog and release-pinned PyPI description
• records the exact local and post-merge validation evidence
• truthfully aligns the machine-readable coverage floor with the enforced 80% gate (83.95% measured)

Validation

• post-merge main CI, build, docs and pinned-verl workflows are green
• 2222 non-GPU/non-network tests passed at 83.95% coverage
• 8 GPU and 15 network tests passed; three pinned-verl conformance tests passed separately
• strict MkDocs and 44 browser-rendered SVG instances across four viewports passed
• release wheel/sdist build and Twine passed; clean core and training installs passed
• frozen calculator SHA-256 remains 53fc1d4d5b7adee09618d77ad62d4086ba56b78569832d6fc7c3bcd5c2695bbc

No tag is created until this exact release head and its required workflows are green.