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/jwt.js

@@ -0,0 +1,51 @@
+/**
+ * JWT HS256 minimale (niente dipendenze). Stessa logica del worker
+ * Cloudflare precedente: stesso token formato, stessa firma, stessa
+ * verifica. L'app desktop non distingue.
+ */
+
+import crypto from "node:crypto";
+
+function b64url(buf) {
+  return Buffer.from(buf).toString("base64")
+    .replace(/=+$/, "").replace(/\+/g, "-").replace(/\//g, "_");
+}
+
+function b64urlDecode(s) {
+  s = s.replace(/-/g, "+").replace(/_/g, "/");
+  s += "=".repeat((4 - (s.length % 4)) % 4);
+  return Buffer.from(s, "base64");
+}
+
+function hmac(secret, data) {
+  return crypto.createHmac("sha256", secret).update(data).digest();
+}
+
+export function signJwt(claims, secret) {
+  const head = b64url(JSON.stringify({ alg: "HS256", typ: "JWT" }));
+  const body = b64url(JSON.stringify(claims));
+  const sig = b64url(hmac(secret, `${head}.${body}`));
+  return `${head}.${body}.${sig}`;
+}
+
+export function verifyJwt(token, secret) {
+  if (typeof token !== "string") return null;
+  const parts = token.split(".");
+  if (parts.length !== 3) return null;
+  const [head, body, sig] = parts;
+  const expected = b64url(hmac(secret, `${head}.${body}`));
+  // confronto a tempo costante
+  if (sig.length !== expected.length) return null;
+  let diff = 0;
+  for (let i = 0; i < sig.length; i++) diff |= sig.charCodeAt(i) ^ expected.charCodeAt(i);
+  if (diff !== 0) return null;
+  try {
+    const claims = JSON.parse(b64urlDecode(body).toString("utf-8"));
+    if (typeof claims.exp === "number" && claims.exp < Math.floor(Date.now() / 1000)) {
+      return null;
+    }
+    return claims;
+  } catch {
+    return null;
+  }
+}