fix(studio): probe uses service's own knownModels first, not global default

buildModelCandidates prioritized the global configModel (kimi-k2.5)
over service-specific models, causing MiniMax probe to try kimi-k2.5
on MiniMax's endpoint. Now uses knownModels[0] as preferredModel
for services that have them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/studio/src/api/server.ts

@@ -442,8 +442,11 @@ async function probeServiceCapabilities(args: {
     };
   }
   const discoveredModels = modelsResponse.models;
+  // For services with knownModels, use their first model as top candidate — not the global default
+  const preset = resolveServicePreset(baseService);
+  const serviceFirstModel = preset?.knownModels?.[0];
   const modelCandidates = buildModelCandidates({
-    preferredModel: args.preferredModel,
+    preferredModel: args.preferredModel ?? serviceFirstModel,
     configModel: typeof llm.defaultModel === "string" ? llm.defaultModel : typeof llm.model === "string" ? llm.model : undefined,
     envModel,
     discoveredModels,