fix(model-picker): hide models from providers without auth configured

Previously, models from unconfigured providers were shown with an
"auth missing" hint, flooding the picker with 900+ unusable entries.

Now addModelSelectOption early-returns when the provider has no auth,
so only usable models appear in /models and the web chat dropdown.

Fixes #74423

src/flows/model-picker.ts

@@ -295,7 +295,7 @@ function addModelSelectOption(params: {
     hints.push(routeHint);
   }
   if (!params.hasAuth(params.entry.provider)) {
-    hints.push("auth missing");
+    return;
   }
   const label = params.literalPrefixProviders.has(normalizeProviderId(params.entry.provider))
     ? `${params.entry.provider}/${params.entry.id}`