Add SDK parity and local evidence gates

[haochencheng]

Summary

Validation

• bash scripts/ci/pr_checks.sh

Public SDK Contract Checklist

• Public examples use SYNAPSE_AGENT_KEY.
• Public docs/examples point to staging, Arbitrum Sepolia, and MockUSDC where environment details are needed.
• Fixed-price examples pass discovered prices as strings.
• Token-metered LLM examples use invoke_llm() / invokeLlm() without cost_usdc / costUsdc.
• Public SynapseAuth / SynapseProvider returns use named models/interfaces, not raw maps.
• No private keys, seed phrases, credentials, or production tokens are committed.