fix: ensure tool parameters schema is always a valid JSON Schema object

Problem: OpenAI API error 'got type: None' when tool has no/invalid parameters

Solution: Add guard to explicitly create empty object schema with description when no parameters exist

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/lib/ai-agent/tool-executor-agent.ts

@@ -95,7 +95,12 @@ export function createToolDefinition(tool: Tool) {
   const parameters = Array.isArray(tool.parameters)
     ? (tool.parameters as unknown as TPMJSParameter[])
     : [];
-  const schema = tpmjsParamsToZodSchema(parameters);
+
+  // Ensure we have a valid schema - if no parameters, use an empty object with explicit additionalProperties
+  const schema =
+    parameters.length > 0
+      ? tpmjsParamsToZodSchema(parameters)
+      : z.object({}).describe('No parameters required');
 
   return aiTool({
     description: tool.description,