* fix: serve props JSON for /api data requests via middleware rewrite
The /api/:path* -> /ipa/:path* rewrite in next.config.mjs is applied by
Vercel's routing to client-side props fetches
(/_next/data/<buildId>/api/....json), but the data-request context is
lost and the prerendered page HTML is returned instead of JSON
(vercel/next.js#39669). The router then never receives pageProps, so the
API sidebar stays collapsed and the tab title shows undefined until a
full reload. This half of the bug only occurs on Vercel infrastructure;
the dev server and next start resolve rewrites for data requests
correctly, and #900 fixed only the /ipa redirect half.
Middleware rewrites preserve data-request semantics, so rewrite /api/*
to /ipa/* in middleware for data requests only (x-nextjs-data header).
Regular page requests fall through to the existing config rewrites, and
the /ipa -> /api canonical redirect is unchanged.
* fix: move /api data-request rewrite into existing proxy.js
Next 16 uses proxy.js and rejects builds where both middleware.js and
proxy.js exist; this repo already had src/proxy.js for the
/docs-static/_next asset rewrite. Fold the /api -> /ipa data-request
rewrite into it and drop middleware.js. Verified the proxy intercepts:
data responses now carry x-middleware-rewrite: /ipa/... and JSON bodies.
* fix: map bare api.json data requests to ipa/introduction.json
The raw data-path fallback rewrote /_next/data/<build>/api.json to
/_next/data/<build>/ipa.json, but there is no /ipa index page; mirror
the /api -> /ipa/introduction rewrite instead.
