fix(setup): stop presenting ChatGPT OAuth as the default voice fallback

Doctor and dev-fresh told every user without an OpenAI key that voice could
use ChatGPT OAuth, whether or not Codex was installed. Say voice is off
until a key is added or a Codex sign-in is selected, and mark that path
experimental.

scripts/setup-doctor.mjs

@@ -178,7 +178,7 @@ export function buildCapabilitySummary(
     flights,
     voice: configured('OPENAI_API_KEY')
       ? 'available'
-      : 'ChatGPT/Codex OAuth can be selected at runtime',
+      : 'off until an OpenAI key is added, or a Codex ChatGPT sign-in is selected in Provider Settings (experimental)',
     vessels: configured('AISSTREAM_API_KEY') ? 'live AISStream feed' : 'off until an AISStream key is added',
     fires: configured('FIRMS_MAP_KEY') ? 'live NASA FIRMS feed' : 'off until a FIRMS key is added',
     traffic: configured('TOMTOM_API_KEY') ? 'live TomTom flow' : 'built-in traffic simulation',