fix: add missing errors utility and fix seed timestamp casting

- Add apps/api/src/utils/errors.ts with AppError class
- Fix seed.ts timestamp casting for calendario_fiscal

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/utils/errors.ts

@@ -0,0 +1,10 @@
+export class AppError extends Error {
+  constructor(
+    public statusCode: number,
+    public message: string,
+    public isOperational = true
+  ) {
+    super(message);
+    Object.setPrototypeOf(this, AppError.prototype);
+  }
+}