Revert mint path to pre-browser PKCE baseline (2e833f2).

Restore HTTP-only SSO OAuth with curl_cffi then std requests fallback;
remove browser PKCE prefer/fallback knobs and mint_from_sso_browser.

config.json

@@ -40,9 +40,6 @@
     "cpa_push_required": false,
     "cpa_prefer_sso_oauth": true,
     "cpa_require_referrer": true,
-    "cpa_prefer_browser_mint": false,
-    "cpa_allow_browser_fallback": false,
-    "cpa_browser_mint_timeout_sec": 90,
     "cpa_allow_device_fallback": false,
     "mint_proxy": "",
     "mint_timeout_sec": 300,