Polymarket API endpoint is deprecated and has already been sunset

[houtanb]

$ curl -sS -D - -o /dev/null 'https://gamma-api.polymarket.com/markets'
HTTP/2 200
date: Wed, 27 May 2026 18:48:20 GMT
content-type: application/json
vary: Accept-Encoding
vary: Origin
deprecation: true
sunset: Fri, 01 May 2026 00:00:00 GMT
warning: 299 - "use /markets/keyset"
set-cookie: __cf_bm=hINOrzhSSOJxTtMmSu4aqJDX3hiR69HOLQXfQKPnvXY-1779907700.875454-1.0.1.1-QPd7s1DeCXX2tYRKc1GUzHPeb2x5MCyqEFLR2Daf2P5KezrWcY_uRw53chv97B1tUxrKQkB73cB9RnDzVJob1hZB9U0MU4pNoPHQwjfhemMa_MTcsY5bv2Ay2wWWfomP; HttpOnly; SameSite=None; Secure; Path=/; Domain=polymarket.com; Expires=Wed, 27 May 2026 19:18:20 GMT
age: 219
last-modified: Wed, 27 May 2026 18:44:49 GMT
expires: Wed, 27 May 2026 18:53:20 GMT
cache-control: public, max-age=300
cf-cache-status: HIT
strict-transport-security: max-age=7776000; includeSubDomains
server: cloudflare
cf-ray: a027317a7947e1cd-MRS
alt-svc: h3=":443"; ma=86400

We should switch to the /markets/keyset endpoint per the above:

deprecation: true
sunset: Fri, 01 May 2026 00:00:00 GMT
warning: 299 - "use /markets/keyset"