Maker: duplica ricetta e durata loop predefinita (#52, #49)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/frontend/flask_app/templates/maker/recipe_editor.html

@@ -526,7 +526,8 @@ function recipeEditor() {
     currentVersion: {{ (recipe.current_version.version_number if recipe and recipe.current_version else 0)|tojson }},
 
     // ---- Measurement interval ----
-    measurementIntervalMinutes: {{ (recipe.measurement_interval_minutes if recipe and recipe.measurement_interval_minutes else 'null')|tojson }},
+    // #49: a new recipe starts from the system default duration (default_interval), an existing one never does
+    measurementIntervalMinutes: {{ (recipe.measurement_interval_minutes if recipe and recipe.measurement_interval_minutes else (default_interval if not recipe and default_interval else 'null'))|tojson }},
 
     // ---- Rules of measurement (points 8 and 9) ----
     // A new recipe forbids typing: the caliper is the instrument, and permission