feat: expose verify share safety

[danielgwilson]

Summary

• add machine-readable shareSafety to mimetic verify results
• classify verified runs as share_ready, local_only, or blocked
• fail closed in mimetic feedback when evidence is valid local proof but not public-promotable
• document the verify-vs-share-ready boundary across README and contracts

Proof

• pnpm vitest run tests/run.test.ts tests/feedback.test.ts
• pnpm typecheck
• pnpm release:check
• direct CLI proof: dry-run verify returns shareSafety: share_ready
• direct CLI proof: synthetic raw-screenshot posture verifies ok: true, returns shareSafety: local_only, and feedback issue refuses with MIMETIC_FEEDBACK_SHARE_SAFETY_BLOCKED

Public boundary

Uses only synthetic fixture data and generic public-safe docs. No private adopter names, private screenshots, credentials, or local runtime artifacts are included.