feat: add MCP OAuth evidence capture

[creatornader]

Summary

• add opt-in MCP/OAuth authorization evidence capture in @atrib/mcp sidecars
• add generic OAuth/MCP evidence verification with DPoP, introspection, and settlement-level evidence[] support
• add the local integration harness, §5.5.6 OAuth conformance corpus, explorer rendering, and docs/spec/ADR updates

Verification

• pnpm --filter @atrib/mcp typecheck
• pnpm --filter @atrib/verify typecheck
• pnpm --filter @atrib/integration typecheck
• pnpm --filter @atrib/mcp test -- middleware.test.ts local-sidecar.test.ts
• pnpm --filter @atrib/verify test -- verify-record.test.ts verifier.test.ts oauth-evidence-conformance.test.ts
• pnpm --filter @atrib/integration test -- mcp-oauth-evidence.test.ts
• pnpm --filter @atrib/integration mcp-oauth-evidence
• pnpm exec vitest run apps/dashboard/test/overview-copy.test.mjs
• pnpm doc-sync
• git diff --check