feat: add comprehensive filter UI with chip-based dropdowns

Add advanced filtering with category, tags (multi-select), icon, season,
and favorites filters. All filters use consistent chip-based dropdown UI
with type-to-search functionality.

New Components:
- TagChip.svelte: Reusable chip component with selected/removable states
- CategoryFilter.svelte: Single-select category with chip dropdown
- TagFilter.svelte: Multi-select tags with AND logic and chip dropdown
- IconFilter.svelte: Single-select emoji icon with chip dropdown
- SeasonFilter.svelte: Multi-select months with chip dropdown
- FavoritesFilter.svelte: Toggle for favorites-only filtering
- FilterPanel.svelte: Container with responsive layout and mobile toggle

Search Component:
- Integrated FilterPanel with all filter types
- Added applyNonTextFilters() for category/tags/icon/season/favorites
- Implemented favorites filter logic (recipe.isFavorite check)
- Made tags/icons reload reactively when language changes with $effect
- Updated buildSearchUrl() for comma-separated array parameters
- Passed categories and isLoggedIn props to enable all filters

Server API:
- Both /api/rezepte/search and /api/recipes/search support:
  - Multi-tag AND logic using MongoDB $all operator
  - Multi-season filtering using MongoDB $in operator
  - Backwards compatible with single tag/season parameters
- Updated search page server load to parse tag/season arrays

UI/UX:
- Filters display inline on wide screens with 2rem gap
- Mobile: collapsible with subtle toggle button and slide-down animation
- Chip-based dropdowns appear on focus with filtering as you type
- Selected items display as removable chips below inputs (no background)
- Centered labels on desktop, left-aligned on mobile
- Reduced vertical spacing on mobile (0.3rem gap)
- Max-width constraints: 500px for filters, 600px for panel on mobile
- Consistent naming: "Tags" and "Icon" instead of German translations

src/routes/[recipeLang=recipeLang]/+page.svelte

@@ -101,7 +101,7 @@ h1{
 <h1>{labels.title}</h1>
 <p class=subheading>{labels.subheading}</p>
 
-<Search lang={data.lang} recipes={data.all_brief} onSearchResults={handleSearchResults}></Search>
+<Search lang={data.lang} recipes={data.all_brief} categories={categories} isLoggedIn={!!data.session?.user} onSearchResults={handleSearchResults}></Search>
 
 {#if seasonRecipes.length > 0}
 	<LazyCategory title={labels.inSeason} eager={true}>

src/routes/[recipeLang=recipeLang]/search/+page.server.ts

@@ -7,18 +7,41 @@ export const load: PageServerLoad = async ({ url, fetch, params, locals }) => {
 
     const query = url.searchParams.get('q') || '';
     const category = url.searchParams.get('category');
-    const tag = url.searchParams.get('tag');
+
+    // Handle both old and new tag params
+    const singleTag = url.searchParams.get('tag');
+    const multipleTags = url.searchParams.get('tags');
+    const tags = multipleTags
+        ? multipleTags.split(',').map(t => t.trim()).filter(Boolean)
+        : (singleTag ? [singleTag] : []);
+
     const icon = url.searchParams.get('icon');
-    const season = url.searchParams.get('season');
+
+    // Handle multiple seasons
+    const singleSeason = url.searchParams.get('season');
+    const multipleSeasons = url.searchParams.get('seasons');
+    const seasons = multipleSeasons
+        ? multipleSeasons.split(',').map(s => s.trim()).filter(Boolean)
+        : (singleSeason ? [singleSeason] : []);
+
     const favoritesOnly = url.searchParams.get('favorites') === 'true';
 
     // Build API URL with filters
     const apiUrl = new URL(`${apiBase}/search`, url.origin);
     if (query) apiUrl.searchParams.set('q', query);
     if (category) apiUrl.searchParams.set('category', category);
-    if (tag) apiUrl.searchParams.set('tag', tag);
+
+    // Pass as comma-separated to API
+    if (tags.length > 0) {
+        apiUrl.searchParams.set('tags', tags.join(','));
+    }
+
     if (icon) apiUrl.searchParams.set('icon', icon);
-    if (season) apiUrl.searchParams.set('season', season);
+
+    if (seasons.length > 0) {
+        apiUrl.searchParams.set('seasons', seasons.join(','));
+    }
+
     if (favoritesOnly) apiUrl.searchParams.set('favorites', 'true');
 
     try {
@@ -39,9 +62,9 @@ export const load: PageServerLoad = async ({ url, fetch, params, locals }) => {
             error: searchResponse.ok ? null : results.error || 'Search failed',
             filters: {
                 category,
-                tag,
+                tags, // Now an array
                 icon,
-                season,
+                seasons, // Now an array
                 favoritesOnly
             }
         };
@@ -53,9 +76,9 @@ export const load: PageServerLoad = async ({ url, fetch, params, locals }) => {
             error: 'Search failed',
             filters: {
                 category,
-                tag,
+                tags: [],
                 icon,
-                season,
+                seasons: [],
                 favoritesOnly
             }
         };

src/routes/[recipeLang=recipeLang]/search/+page.svelte

@@ -7,6 +7,9 @@
     let current_month = new Date().getMonth() + 1;
 
     const isEnglish = $derived(data.lang === 'en');
+    const categories = $derived(isEnglish
+        ? ["Main course", "Noodle", "Bread", "Dessert", "Soup", "Side dish", "Salad", "Cake", "Breakfast", "Sauce", "Ingredient", "Drink", "Spread", "Biscuits", "Snack"]
+        : ["Hauptspeise", "Nudel", "Brot", "Dessert", "Suppe", "Beilage", "Salat", "Kuchen", "Frühstück", "Sauce", "Zutat", "Getränk", "Aufstrich", "Guetzli", "Snack"]);
     const labels = $derived({
         title: isEnglish ? 'Search Results' : 'Suchergebnisse',
         pageTitle: isEnglish
@@ -17,9 +20,9 @@
             : 'Suchergebnisse in den Bockenschen Rezepten.',
         filteredBy: isEnglish ? 'Filtered by:' : 'Gefiltert nach:',
         category: isEnglish ? 'Category' : 'Kategorie',
-        keyword: isEnglish ? 'Keyword' : 'Stichwort',
+        keywords: isEnglish ? 'Keywords' : 'Stichwörter',
         icon: 'Icon',
-        season: isEnglish ? 'Season' : 'Saison',
+        seasons: isEnglish ? 'Seasons' : 'Monate',
         favoritesOnly: isEnglish ? 'Favorites only' : 'Nur Favoriten',
         searchError: isEnglish ? 'Search error:' : 'Fehler bei der Suche:',
         resultsFor: isEnglish ? 'results for' : 'Ergebnisse für',
@@ -73,25 +76,27 @@
 
 <h1>{labels.title}</h1>
 
-{#if data.filters.category || data.filters.tag || data.filters.icon || data.filters.season || data.filters.favoritesOnly}
+{#if data.filters.category || data.filters.tags?.length > 0 || data.filters.icon || data.filters.seasons?.length > 0 || data.filters.favoritesOnly}
     <div class="filter-info">
         {labels.filteredBy}
-        {#if data.filters.category}{labels.category} "{data.filters.category}"{/if}
-        {#if data.filters.tag}{labels.keyword} "{data.filters.tag}"{/if}
-        {#if data.filters.icon}{labels.icon} "{data.filters.icon}"{/if}
-        {#if data.filters.season}{labels.season} "{data.filters.season}"{/if}
+        {#if data.filters.category}{labels.category}: "{data.filters.category}"{/if}
+        {#if data.filters.tags?.length > 0}{labels.keywords}: {data.filters.tags.join(', ')}{/if}
+        {#if data.filters.icon}{labels.icon}: "{data.filters.icon}"{/if}
+        {#if data.filters.seasons?.length > 0}{labels.seasons}: {data.filters.seasons.join(', ')}{/if}
         {#if data.filters.favoritesOnly}{labels.favoritesOnly}{/if}
     </div>
 {/if}
 
 <Search
     category={data.filters.category}
-    tag={data.filters.tag}
+    tag={data.filters.tags?.[0] || null}
     icon={data.filters.icon}
-    season={data.filters.season}
+    season={data.filters.seasons?.[0] || null}
     favoritesOnly={data.filters.favoritesOnly}
     lang={data.lang}
     recipes={data.allRecipes}
+    categories={categories}
+    isLoggedIn={!!data.session?.user}
     onSearchResults={handleSearchResults}
 />