fix: use inline type definition to fix TypeScript compilation

TypeScript couldn't infer the return type from fileGeneratorTool.execute
since it could be undefined. Instead of using ReturnType, define the
FileGeneratorToolResult type inline in the test file.

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

Co-Authored-By: Claude <[email protected]>

Author: mrjasonroy

src/lib/ai/tools/file-generator/index.test.ts

@@ -22,9 +22,17 @@ vi.mock("logger", () => ({
 
 // Import after mocking
 const { fileGeneratorTool } = await import("./index");
-type FileGeneratorToolResult = Awaited<
-  ReturnType<typeof fileGeneratorTool.execute>
->;
+
+type FileGeneratorToolResult = {
+  files: {
+    url: string;
+    filename: string;
+    mimeType: string;
+    size: number;
+  }[];
+  description?: string;
+  guide?: string;
+};
 
 describe("fileGeneratorTool.execute", () => {
   beforeEach(() => {