feat: publish governance platform customer packages

[captjt]

Summary

Adds the deployment-side customer package, chart, and docsite release surface for Governance Platform v0.1.0.

• Adds Helm CI for charts, examples, registry overrides, and release manifests
• Adds release-platform-package.yaml for publishing charts, packages, checksums, attestations, and GitHub releases
• Adds docs-site source scaffold for ReadMe versioned documentation
• Adds release manifest schema with manual validation evidence contract
• Mirrors chart image registry override support from infrastructure

Validation

• YAML syntax validated locally
• JSON schema syntax validated locally
• actionlint passed for touched workflows
• Helm dependency build/lint/template validation passed from a clean temp checkout
• Local docsite markdown links validated

Cross-Repository PR Set

• Governance Studio image workflow: https://github.com/eqtylab/governance-studio/pull/639
• Governance Backend image workflows: https://github.com/eqtylab/governance-backend/pull/289
• Integrity Service image workflow: https://github.com/eqtylab/integrity-monorepo/pull/1643
• Infrastructure release orchestration and chart source of truth: https://github.com/eqtylab/governance-studio-infrastructure/pull/70
• Deployment customer package, chart, and docs publication: feat: publish governance platform customer packages #9

Suggested Merge Order

1. Component image workflow PRs: Studio, Backend, Integrity
2. Infrastructure orchestration PR
3. Deployment publication PR

This PR is the customer-facing publication surface. It can be reviewed in parallel, but final publication should happen only after the infrastructure release candidate flow and manual validation evidence are accepted.