docs: add acceptance review lane ADR

[aryeko]

Summary

• add ADR 0034 to settle the acceptance/review lane and verifier boundary introduced by PR Clarify verification lane product and design boundaries #82
• index the ADR and preserve existing ADR numbering rather than reusing 0029
• add lightweight design backrefs from the core, provider, and security docs

Boundary

• docs-only
• no runtime/config/schema/provider changes
• does not claim SEC-2 progress or freeze acceptance verdict event families

Verification

• pnpm exec prettier --write docs/design/decisions/0034-acceptance-review-lane.md docs/design/decisions/README.md docs/design/README.md docs/design/core/README.md docs/design/core/bootstrap.md docs/design/core/orchestration.md docs/design/core/authorization.md docs/design/core/plan-intake.md docs/design/core/records.md docs/design/contracts/providers.md docs/design/security-model.md
• pnpm links:check
• git diff --check
• pnpm check