feat: add PWA offline support for recipe pages

- Add service worker with caching for build assets, static files, images, and pages
- Add IndexedDB storage for recipes (brief and full data)
- Add offline-db API endpoint for bulk recipe download
- Add offline sync button component in header
- Add offline-shell page for direct navigation fallback
- Pre-cache __data.json for client-side navigation
- Add +page.ts universal load functions with IndexedDB fallback
- Add PWA manifest and icons for installability
- Update recipe page to handle missing data gracefully

src/routes/api/rezepte/offline-db/+server.ts

@@ -0,0 +1,79 @@
+import { json, type RequestHandler } from '@sveltejs/kit';
+import type { BriefRecipeType, RecipeModelType } from '../../../../types/types';
+import { Recipe } from '../../../../models/Recipe';
+import { dbConnect } from '../../../../utils/db';
+
+export const GET: RequestHandler = async () => {
+	await dbConnect();
+
+	// Fetch brief recipes (for lists/filtering)
+	const briefRecipes = await Recipe.find(
+		{},
+		'name short_name tags category icon description season dateModified'
+	).lean() as BriefRecipeType[];
+
+	// Fetch full recipes with populated base recipe references
+	const fullRecipes = await Recipe.find({})
+		.populate({
+			path: 'ingredients.baseRecipeRef',
+			select: 'short_name name ingredients translations',
+			populate: {
+				path: 'ingredients.baseRecipeRef',
+				select: 'short_name name ingredients translations',
+				populate: {
+					path: 'ingredients.baseRecipeRef',
+					select: 'short_name name ingredients translations'
+				}
+			}
+		})
+		.populate({
+			path: 'instructions.baseRecipeRef',
+			select: 'short_name name instructions translations',
+			populate: {
+				path: 'instructions.baseRecipeRef',
+				select: 'short_name name instructions translations',
+				populate: {
+					path: 'instructions.baseRecipeRef',
+					select: 'short_name name instructions translations'
+				}
+			}
+		})
+		.lean() as RecipeModelType[];
+
+	// Map populated refs to resolvedRecipe field (same as individual item endpoint)
+	function mapBaseRecipeRefs(items: any[]): any[] {
+		if (!items) return items;
+		return items.map((item: any) => {
+			if (item.type === 'reference' && item.baseRecipeRef) {
+				const resolvedRecipe = { ...item.baseRecipeRef };
+
+				if (resolvedRecipe.ingredients) {
+					resolvedRecipe.ingredients = mapBaseRecipeRefs(resolvedRecipe.ingredients);
+				}
+				if (resolvedRecipe.instructions) {
+					resolvedRecipe.instructions = mapBaseRecipeRefs(resolvedRecipe.instructions);
+				}
+
+				return { ...item, resolvedRecipe };
+			}
+			return item;
+		});
+	}
+
+	const processedFullRecipes = fullRecipes.map((recipe) => {
+		const processed = { ...recipe };
+		if (processed.ingredients) {
+			processed.ingredients = mapBaseRecipeRefs(processed.ingredients);
+		}
+		if (processed.instructions) {
+			processed.instructions = mapBaseRecipeRefs(processed.instructions);
+		}
+		return processed;
+	});
+
+	return json({
+		brief: JSON.parse(JSON.stringify(briefRecipes)),
+		full: JSON.parse(JSON.stringify(processedFullRecipes)),
+		syncedAt: new Date().toISOString()
+	});
+};