Setup commercial launch: licenze + backend Cloudflare Worker

Client (Python/JS):
- core/license.py: attivazione, validazione, deactivate (HTTP client + JWT decode)
- core/config.py: campi license_* + URL endpoint + costanti grace/revalidate
- api/bridge.py: get_init_data ritorna license status; activate_license/
  deactivate_license/revalidate_license/open_purchase_page
- check_update riscritto: punta a musictools.djluza.com/api/latest con
  Bearer token, URL di download firmato dal server solo se licensed
- webui: schermata di attivazione bloccante all'avvio; sezione Licenza
  in Impostazioni con verifica/disattiva

Backend (server/):
- Cloudflare Worker + D1 + R2 (vedi server/README.md)
- Endpoints: /api/license/{activate,validate,deactivate}, /api/latest,
  /api/webhook/lemonsqueezy, /api/health
- JWT HS256 con rotazione; max 3 attivazioni/licenza
- Generazione licenze via webhook Lemon Squeezy + email Resend
- Schema D1 in migrations/0001_init.sql

Memory: nuova musictools-commercial-launch.md, rimosso pending obsoleto

NON taggare finche backend non e' deployato (l'app e' bloccante)

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

webui/css/style.css

@@ -1256,3 +1256,157 @@ input[type="number"]::-webkit-inner-spin-button {
     max-height: none;
   }
 }
+
+/* ============================================================
+   SCHERMATA ATTIVAZIONE LICENZA
+   ============================================================ */
+.activate-screen {
+  position: fixed;
+  inset: 0;
+  z-index: 9999;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 40px 20px;
+  background:
+    radial-gradient(ellipse at top, rgba(29, 185, 84, 0.18), transparent 60%),
+    linear-gradient(180deg, #0a0a0a 0%, #060606 100%);
+  overflow: auto;
+}
+
+.activate-screen[hidden] { display: none; }
+
+.activate-card {
+  width: 100%;
+  max-width: 460px;
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-radius: 18px;
+  padding: 40px 36px;
+  box-shadow: 0 30px 80px rgba(0, 0, 0, 0.5);
+  text-align: center;
+}
+
+.activate-logo {
+  width: 72px;
+  height: 72px;
+  margin: 0 auto 20px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  border-radius: 22px;
+  background: linear-gradient(135deg, #1db954 0%, #137a37 100%);
+  color: #fff;
+  font-size: 36px;
+  box-shadow: 0 12px 30px rgba(29, 185, 84, 0.4);
+}
+
+.activate-title {
+  margin: 0 0 8px;
+  font-size: 22px;
+  font-weight: 800;
+  color: var(--text);
+}
+
+.activate-sub {
+  margin: 0 0 28px;
+  font-size: 13.5px;
+  color: var(--text-muted);
+  line-height: 1.55;
+}
+
+.activate-form {
+  text-align: left;
+}
+
+.activate-form .field {
+  margin-bottom: 14px;
+}
+
+.activate-error {
+  background: rgba(220, 53, 69, 0.12);
+  border: 1px solid rgba(220, 53, 69, 0.4);
+  color: #ff6b7a;
+  padding: 10px 14px;
+  border-radius: 12px;
+  font-size: 13px;
+  margin: 6px 0 14px;
+}
+
+.activate-actions {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  margin-top: 6px;
+}
+
+.activate-actions .btn {
+  width: 100%;
+  justify-content: center;
+}
+
+.activate-foot {
+  margin-top: 24px;
+  text-align: center;
+  font-size: 12px;
+  color: var(--text-muted);
+}
+
+.activate-foot a {
+  color: var(--accent);
+  text-decoration: none;
+}
+
+.activate-foot a:hover { text-decoration: underline; }
+
+/* ============================================================
+   IMPOSTAZIONI > LICENZA
+   ============================================================ */
+.license-box {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin-bottom: 14px;
+}
+
+.lic-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: baseline;
+  padding: 8px 0;
+  border-bottom: 1px dashed var(--divider);
+  font-size: 13.5px;
+}
+
+.lic-row:last-child { border-bottom: none; }
+
+.lic-row span {
+  color: var(--text-muted);
+  text-transform: uppercase;
+  letter-spacing: 0.6px;
+  font-size: 11px;
+  font-weight: 600;
+}
+
+.lic-row strong {
+  color: var(--text);
+  font-weight: 700;
+  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
+  word-break: break-all;
+}
+
+.lic-warn {
+  padding: 14px;
+  border-radius: 12px;
+  background: rgba(220, 53, 69, 0.12);
+  border: 1px solid rgba(220, 53, 69, 0.35);
+  color: #ff6b7a;
+  font-weight: 700;
+  text-align: center;
+}
+
+.license-actions {
+  display: flex;
+  gap: 10px;
+  flex-wrap: wrap;
+}