feat(recipes): add recently opened sort with modal open tracking

Track recipe modal opens in a separate stats file (never touching recipe
JSON/EXIF), expose a fire-and-forget POST endpoint, and add an 'opened'
sort that hides never-opened recipes as a true recently-opened view.
Includes i18n for all locales and backend/frontend tests.

static/js/components/RecipeModal.js

@@ -306,6 +306,14 @@ class RecipeModal {
         modalManager.showModal('recipeModal');
 
         if (this.recipeId) {
+            // Fire-and-forget: record this open for the "Recently Opened"
+            // sort. Tracking must never disturb the modal, so failures are
+            // swallowed.
+            fetch(`/api/lm/recipe/${encodeURIComponent(this.recipeId)}/opened`, {
+                method: 'POST',
+                keepalive: true,
+            }).catch(() => {});
+
             const hydrationRequestId = ++this.recipeHydrationRequestId;
             const requestEditVersions = this.captureLocalEditVersions();
             this.hydrateRecipeDetails(