fix(server): CORS whitelist still references opencode.ai after rebrand

[ch1lam]

Description

The CORS origin regex in packages/opencode/src/server/middleware.ts still matches opencode.ai instead of mimo.xiaomi.com. After the rebrand, the web UI and desktop app hosted on mimo.xiaomi.com cannot make cross-origin requests to the server because the CORS check rejects their origin.

Current behavior

if (/^https:\/\/([a-z0-9-]+\.)*opencode\.ai$/.test(input)) return input

Expected behavior

if (/^https:\/\/([a-z0-9-]+\.)*mimo\.xiaomi\.com$/.test(input)) return input

Fix

#139