Fix Pinterest Inspired Design harvest readiness

[freshtechbro]

Summary

• Harden Pinterest browser-native Inspired Design harvest so concrete pin evidence can be collected while chrome-only references remain diagnostic.
• Block Canvas continuation unless typed next-step guidance is ready, and prevent rejected Pinterest references from leaking into design-facing artifacts.
• Add regression coverage for Pinterest URL handling, diagnostic-only harvests, guidance context, handoff gating, and artifact contamination boundaries.

Real workflow evidence

• Ran a real Pinterest harvest for a design agency studio landing page with extension mode, user-authorized cookies, required visual evidence, and browser helper challenge mode.
• Final artifact: /tmp/odb-design-agency-final-postfix3/inspiredesign/420c9d2c-5f58-4ba9-be30-58448bb00dd5
• Outcome: 5 Pinterest pin URLs accepted, 5 screenshots captured, 0 ranked design-ready references, readiness diagnostic_only, Canvas continuation blocked, rejected pin titles and URLs did not leak into design-facing files.

Review

• RepoPrompt review merge-review-397FF3 found no P0/P1 merge blockers.

Test plan

• npm run typecheck -- --pretty false
• npm run lint
• npm run build
• npm run extension:build
• npm run version:check
• git diff --check
• npm run test