Disable browser PKCE mint by default.

User does not want web/browser casting; HTTP-only unless
cpa_allow_browser_fallback is explicitly re-enabled.

config.json

@@ -41,7 +41,7 @@
     "cpa_prefer_sso_oauth": true,
     "cpa_require_referrer": true,
     "cpa_prefer_browser_mint": false,
-    "cpa_allow_browser_fallback": true,
+    "cpa_allow_browser_fallback": false,
     "cpa_browser_mint_timeout_sec": 90,
     "cpa_allow_device_fallback": false,
     "mint_proxy": "",