Add x402station preflight example

[sF1nX]

Summary

• Add a TypeScript AgentKit example that calls Preflight by x402station.io before invoking the existing x402 payment action
• Demonstrate fail-closed handling for hard endpoint risk signals before PAYMENT-SIGNATURE is signed
• Document trial vs paid preflight usage and keep softer warnings as policy inputs, not automatic failures

Validation

• pnpm --dir /Users/airbit/forks/agentkit/typescript install --frozen-lockfile
• pnpm --dir /Users/airbit/forks/agentkit/typescript --filter @coinbase/x402station-preflight-agentkit-example test:types
• pnpm --dir /Users/airbit/forks/agentkit/typescript --filter @coinbase/x402station-preflight-agentkit-example lint
• pnpm --dir /Users/airbit/forks/agentkit/typescript --filter @coinbase/x402station-preflight-agentkit-example format:check
• pnpm --dir /Users/airbit/forks/agentkit/typescript run lint
• pnpm --dir /Users/airbit/forks/agentkit/typescript run format:check

Note: running pnpm install also cleaned a stale lockfile importer for examples/register, which is no longer present in the workspace tree.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2