fix(studio): increase probe maxTokens to 248 for thinking models

maxTokens: 5 caused thinking models (MiniMax M2.7) to exhaust all
tokens on reasoning with no text output, failing the probe even
with a valid key.

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

packages/studio/src/api/server.ts

@@ -478,7 +478,7 @@ async function probeServiceCapabilities(args: {
       } as ProjectConfig["llm"]);
 
       try {
-        await chatCompletion(client, model, [{ role: "user", content: "ping" }], { maxTokens: 5 });
+        await chatCompletion(client, model, [{ role: "user", content: "hi" }], { maxTokens: 248 });
         const models = discoveredModels.length > 0
           ? discoveredModels
           : [{ id: model, name: model }];