app: relay thinking false to server (#13319)

This fixes a bug where disabling thinking on deepseek-v3.1 did not stop the model from thinking.

When thinking is not defined it should not be sent to the server since this will cause error responses in some cases where the model does not support thinking. However if it is defined as false it should still be sent.

app/ui/app/src/api.ts

@@ -204,12 +204,10 @@ export async function* sendMessage(
     data: uint8ArrayToBase64(att.data),
   }));
 
-  // Only send think parameter when actually requesting thinking
-  // Don't send false as it causes issues with some providers
+  // Send think parameter when it's explicitly set (true, false, or a non-empty string).
   const shouldSendThink =
     think !== undefined &&
-    ((typeof think === "boolean" && think) ||
-      (typeof think === "string" && think !== ""));
+    (typeof think === "boolean" || (typeof think === "string" && think !== ""));
 
   const response = await fetch(`${API_BASE}/api/v1/chat/${chatId}`, {
     method: "POST",