Add decision-scoped data readiness

[davidahmann]

Outcome

Adds a decision-scoped data-readiness method across discovery, design, evaluation, release, and operation.

What changed

• Adds four-plane data readiness guidance, assessment, machine-readable manifest, preparation blueprint, and drift operating contract.
• Adds CTX-006 through CTX-009, semantic validation, release binding, migration guidance, and adversarial tests.
• Integrates the method into the public Guide, lifecycle playbooks, optional skills, site navigation, and invoice reference.
• Bumps the release metadata to v1.16.0.

Validation

• npm ci --ignore-scripts
• npm test
• git diff --check
• npm audit --audit-level=high

All pass locally. Unrelated untracked launch assets remain excluded.