refactor: reorganize project structure and improve user command handling

cmd/register.ts

@@ -0,0 +1,18 @@
+import { ChatInputCommandInteraction, SlashCommandBuilder } from "discord.js";
+import { db } from "../db/db";
+
+export const data = new SlashCommandBuilder()
+    .setName("register")
+    .setDescription("create your stereo account");
+
+export const execute = async (interaction: ChatInputCommandInteraction) => {
+    const existingUser = await db.get<{ id: string }>`SELECT id FROM users WHERE id = ${interaction.user.id}`;
+    if (existingUser) {
+        await interaction.reply({ content: "You already have a stereo account.", ephemeral: true });
+        return;
+    }
+    
+    await interaction.reply({ content: "Your stereo account has been created!", ephemeral: true });
+}
+
+export default [data, execute] as const;