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/backend/services/recipe_service.py

@@ -134,6 +134,7 @@ async def create_recipe(
         name=data.name,
         description=data.description,
         image_path=data.image_path,
+        measurement_interval_minutes=data.measurement_interval_minutes,
         created_by=user.id,
     )
     db.add(recipe)
@@ -273,6 +274,8 @@ async def create_new_version(
         update_fields["description"] = data.description
     if data.image_path is not None:
         update_fields["image_path"] = data.image_path
+    if data.measurement_interval_minutes is not None:
+        update_fields["measurement_interval_minutes"] = data.measurement_interval_minutes
     if update_fields:
         await db.execute(
             update(Recipe).where(Recipe.id == recipe_id).values(**update_fields)
@@ -369,6 +372,8 @@ async def update_current_version(
         update_fields["description"] = data.description
     if data.image_path is not None:
         update_fields["image_path"] = data.image_path
+    if data.measurement_interval_minutes is not None:
+        update_fields["measurement_interval_minutes"] = data.measurement_interval_minutes
     if update_fields:
         await db.execute(
             update(Recipe).where(Recipe.id == recipe_id).values(**update_fields)