feat: timer intervallo misura su ricetta + auto-logout per inattività

- Recipe: nuovo campo measurement_interval_minutes (migration 003) con UI nel recipe editor
- Auto-logout: impostazione di sistema configurabile da admin/settings, timer inattività JS
  con warning modale 60s prima del logout, tracking eventi utente throttled
- Navbar: aggiunto link "Impostazioni" per admin (desktop + mobile)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/frontend/flask_app/blueprints/admin.py

@@ -43,6 +43,28 @@ def user_list():
     return render_template("admin/users.html", users=users)
 
 
+@admin_bp.route("/settings")
+@login_required
+@admin_required
+def settings_page():
+    """System settings page."""
+    resp = api_client.get("/api/settings")
+    settings = resp if not isinstance(resp, dict) or not resp.get("error") else {}
+    return render_template("admin/settings.html", settings=settings)
+
+
+@admin_bp.route("/api/settings", methods=["PUT"])
+@login_required
+@admin_required
+def api_update_settings():
+    """Proxy: Update system settings."""
+    data = request.get_json(silent=True) or {}
+    resp = api_client.put("/api/settings", data=data)
+    if isinstance(resp, dict) and resp.get("error"):
+        return jsonify(resp), resp.get("status_code", 500)
+    return jsonify(resp), 200
+
+
 @admin_bp.route("/stations")
 @login_required
 @admin_required

src/frontend/flask_app/blueprints/auth.py

@@ -76,12 +76,18 @@ def login():
             if user.get("theme_pref"):
                 session["theme"] = user["theme_pref"]
 
-            # Carica logo aziendale dalle impostazioni di sistema
+            # Carica impostazioni di sistema
             settings_resp = api_client.get("/api/settings")
             if not settings_resp.get("error"):
                 logo_path = settings_resp.get("company_logo_path")
                 if logo_path:
                     session["company_logo"] = logo_path
+                auto_logout = settings_resp.get("auto_logout_minutes")
+                if auto_logout:
+                    try:
+                        session["auto_logout_minutes"] = int(auto_logout)
+                    except (ValueError, TypeError):
+                        pass
 
             flash(_("Benvenuto, %(name)s!", name=user.get("display_name", username)), "success")