feat: serve OpenAPI discovery at /openapi.json

[brendanjryan]

Adds an /api/openapi.json route that generates an OpenAPI 3.1.0 discovery document using mppx/discovery, plus a Vercel rewrite so https://mpp.dev/openapi.json serves it.

The document describes the site's paid endpoints with x-payment-info metadata for agent discovery.

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Project	Deployment	Actions	Updated (UTC)
mpp	Error		Mar 25, 2026 10:20pm

[brendanjryan]

Redundant — #462 already added the openapi route. Will open a follow-up for just the /openapi.json rewrite.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use configured currency in OpenAPI discovery

The discovery document advertises payment metadata from a hardcoded USDC address here, but the actual /api/ping/paid endpoint charges import.meta.env.VITE_DEFAULT_CURRENCY in src/pages/_api/api/ping/paid.ts. In any deployment where that env var differs (the repository’s .env.example already uses a different address), /openapi.json will publish incorrect x-payment-info, causing clients that rely on discovery to pay with the wrong token and fail when they hit the real Challenge flow.

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