v0.2.0

The register becomes a regression gate, the safest usage becomes the easiest
usage, and a green check can no longer be misread. All three features trace to
the two pilot adoptions and two external reviews of the v0.1 line.

Highlights

• Impact routing — an optional components: map (path globs → invariant
  IDs) plus a pull-request drift gate: touched components must be answered by
  an assurance update, the affected invariant IDs in the PR body, or an
  explicit Assurance impact: none + Reason: statement. Warn-first;
  strict-drift escalates.
• core-lite — a four-file adoption for core repositories (AGENTS.md
  section, AGENTIC_ASSURANCE.md, adoption.yaml with layout: lite, and a
  single assurance.yaml), down from the second pilot's 25-file first
  adoption. Register item shapes stay defined solely by the register schemas.
• Adoption stages + attributable approval — self-declared, self-binding
  adoption_stage: DRAFT | HUMAN_REVIEWED | CONFORMANT; CI checks split into
  structure and conformance (skipped while DRAFT); human_review.approvals
  records who approved, where, and when.
• data-curation promoted from provisional (every §6.4 obligation exercised
  by the second pilot); agent-runtime remains provisional.

Adopter impact / upgrade actions

• Re-pin optional; v0.1.x pins remain valid. Upgrading adopters update
  upstream.version → v0.2.0, upstream.commit → the commit this tag
  points to, and the workflow @ reference in one reviewed change.
• Required-check rename: assurance / validate → assurance / structure
  (plus new assurance / conformance). Update branch-protection settings when
  re-pinning.
• Adoptions without the new optional fields behave byte-identically.

Full changelog: CHANGELOG.md