feat: seed demo character and first locations

apps/api/src/database/seeds/run-seed.ts

@@ -0,0 +1,17 @@
+import { AppDataSource } from '../data-source';
+import { seedVisibleVerticalSlice } from './vertical-slice.seed';
+
+async function runSeed(): Promise<void> {
+  await AppDataSource.initialize();
+
+  try {
+    await seedVisibleVerticalSlice(AppDataSource);
+  } finally {
+    await AppDataSource.destroy();
+  }
+}
+
+void runSeed().catch((error: unknown) => {
+  console.error('Demo seed failed:', error);
+  process.exitCode = 1;
+});