chore(release): prepare 0.5.0 (docs, changelog, checklist, version)

[davidamacey]

Release-prep for 0.5.0 (docs and version only). Does not run make release, push images, tag or publish.

• docs(release): consolidated CHANGELOG.md [0.5.0] (empty [Unreleased] kept), frontend/CHANGELOG.md [0.5.0], docs/releases/v0.5.0.md, rewritten docs/releases/RELEASE_CHECKLIST.md (Cropwright now in images.lock, project acc-v050, post-release org move step without naming the target), and removal of the stale cropwright.lock docs.
• chore(release): version 0.5.0 in VERSION, pyproject, compose OP_IMAGE_TAG defaults, installer and CLI, docs-site package and lock, roadmap, the installer docker shim, the frontend package, lock and Dockerfile VERSION, and the docs that name the current release.

images.lock is untouched (0.4.1 digests, no cropwright row) until make release.

docs/releases/v0.5.0.md has TODO-LIVE markers for the owner to replace before publishing.

Verified: version-consistency, release-build and installer tests (408 passed), check_docs_vs_code.py, naming-leak scan, generate_contracts.py --check, pre-commit --from-ref origin/main, docs-site npm ci && npm run build.