Refactor database handling to require PostgreSQL connection, removing fallback to JSON. Implement error handling for database unavailability in key files. Update .env.example to reflect mandatory DATABASE_URL for local development. Remove Firebase configuration and related code from the project.

recipe.php

@@ -1,6 +1,12 @@
 <?php
 require __DIR__ . '/helpers.php';
 
+try {
+    $allRecipes = load_recipes();
+} catch (DatabaseUnavailableException $e) {
+    handle_database_unavailable($e);
+}
+
 $lang = (isset($_GET['lang']) && strtolower($_GET['lang']) === 'de') ? 'de' : 'en';
 $copy = [
     'en' => [
@@ -46,7 +52,6 @@ $copy = [
 ];
 $t = $copy[$lang];
 
-$allRecipes       = load_recipes();
 $slug             = isset($_GET['slug']) ? trim($_GET['slug']) : '';
 $recipeRaw        = $slug ? load_recipe_by_slug($slug) : null;
 $recipe           = $recipeRaw ? localize_recipe($recipeRaw, $lang) : null;