Riscrivi backend per hosting Node/MariaDB/PM2 (no Cloudflare)

L'utente ha un hosting Virtualmin esistente (musictools.djluza.com)
con Apache + Node 20 + MariaDB + PM2. Tutta l'infrastruttura
Cloudflare (Workers/D1/R2/Pages) e' rimpiazzata con un backend
Express che gira sul server gia' presente, a costo zero.

Cambia:
- server/src/*.ts (Workers) -> server/src/*.js (Node ESM puro)
- D1 (sqlite) -> MariaDB 10.11 via mysql2/promise
- R2 (storage) -> filesystem locale ~/builds/ + signed URL HMAC
- wrangler.toml -> ecosystem.config.cjs (PM2)
- Aggiunto src/migrate.js: runner SQL idempotente

Endpoints invariati - l'app desktop non vede differenze:
- POST /api/license/{activate,validate,deactivate}
- GET  /api/latest, /api/download
- POST /api/webhook/lemonsqueezy
- GET  /api/health

README riscritto con istruzioni complete: creazione DB,
deploy via rsync/git, config Apache reverse proxy via
Virtualmin, gestione PM2, backup, workflow release.

Email rimane su Resend (deliverability) - free tier sufficiente.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/src/db.js

@@ -0,0 +1,30 @@
+import mysql from "mysql2/promise";
+
+const pool = mysql.createPool({
+  host: process.env.DB_HOST || "127.0.0.1",
+  port: Number(process.env.DB_PORT || 3306),
+  user: process.env.DB_USER,
+  password: process.env.DB_PASS,
+  database: process.env.DB_NAME,
+  waitForConnections: true,
+  connectionLimit: 5,
+  queueLimit: 0,
+  charset: "utf8mb4",
+});
+
+export async function query(sql, params = []) {
+  const [rows] = await pool.execute(sql, params);
+  return rows;
+}
+
+export async function one(sql, params = []) {
+  const rows = await query(sql, params);
+  return rows[0] || null;
+}
+
+export async function exec(sql, params = []) {
+  const [result] = await pool.execute(sql, params);
+  return result; // { insertId, affectedRows, ... }
+}
+
+export default pool;