feat(conformance): add agent commerce governance profile

[pshkv]

Summary

• add Agent Commerce Governance Profile v1 for task-market and x402-style machine-payment workflows
• publish executable fixtures for identity registration, capability scope, task modes, reputation gates, auction bid rules, benchmark proof requirements, x402 permit policy, and settlement receipts
• add conformance tests and wire the profile into the fixture suite and docs navigation

Why

Agent-to-agent task markets and machine routers need a pre-action policy boundary before agents bid, claim, submit work, accept deliverables, sign x402 permits, or release settlement. This profile makes SINT's role concrete: not the marketplace or payment rail, but the governance layer that returns typed allow, deny, or escalate decisions before work or money moves.

Validation

• pnpm --filter @pshkv/conformance-tests exec vitest run src/agent-commerce-governance-conformance.test.ts
• pnpm --filter @pshkv/conformance-tests test:fixtures
• pnpm run docs:build
• git diff --check