fix(ai): default tool call arguments to empty object for Google providers

When Google providers return tool calls without an args field (common for
no-argument tools), the arguments field was undefined. This breaks
subsequent API calls that require tool_use.input to be present.

Now defaults to {} when args is missing.

Related: clawdbot/clawdbot#1509

packages/ai/src/providers/google-gemini-cli.ts

@@ -685,7 +685,7 @@ export const streamGoogleGeminiCli: StreamFunction<"google-gemini-cli", GoogleGe
 											type: "toolCall",
 											id: toolCallId,
 											name: part.functionCall.name || "",
-											arguments: part.functionCall.args as Record<string, unknown>,
+											arguments: (part.functionCall.args as Record<string, unknown>) ?? {},
 											...(part.thoughtSignature && { thoughtSignature: part.thoughtSignature }),
 										};