feat: implement database module and service with PostgreSQL integration and migrations support

backend/src/database/database.module.ts

@@ -0,0 +1,10 @@
+import { Module } from "@nestjs/common";
+import { ConfigModule } from "@nestjs/config";
+import { DatabaseService } from "./database.service";
+
+@Module({
+	imports: [ConfigModule],
+	providers: [DatabaseService],
+	exports: [DatabaseService],
+})
+export class DatabaseModule {}