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/api/recipes/search/+server.ts

@@ -8,9 +8,23 @@ export const GET: RequestHandler = async ({ url, locals }) => {
 
   const query = url.searchParams.get('q')?.toLowerCase().trim() || '';
   const category = url.searchParams.get('category');
-  const tag = url.searchParams.get('tag');
+
+  // Support both single tag (backwards compat) and multiple tags
+  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');
+
+  // Support both single season (backwards compat) and multiple seasons
+  const singleSeason = url.searchParams.get('season');
+  const multipleSeasons = url.searchParams.get('seasons');
+  const seasons = multipleSeasons
+    ? multipleSeasons.split(',').map(s => parseInt(s.trim())).filter(n => !isNaN(n))
+    : (singleSeason ? [parseInt(singleSeason)].filter(n => !isNaN(n)) : []);
+
   const favoritesOnly = url.searchParams.get('favorites') === 'true';
 
   try {
@@ -24,19 +38,18 @@ export const GET: RequestHandler = async ({ url, locals }) => {
       dbQuery['translations.en.category'] = category;
     }
 
-    if (tag) {
-      dbQuery['translations.en.tags'] = { $in: [tag] };
+    // Multi-tag AND logic: recipe must have ALL selected tags
+    if (tags.length > 0) {
+      dbQuery['translations.en.tags'] = { $all: tags };
     }
 
     if (icon) {
       dbQuery.icon = icon;  // Icon is the same for both languages
     }
 
-    if (season) {
-      const seasonNum = parseInt(season);
-      if (!isNaN(seasonNum)) {
-        dbQuery.season = { $in: [seasonNum] };  // Season is the same for both languages
-      }
+    // Multi-season OR logic: recipe in any selected season
+    if (seasons.length > 0) {
+      dbQuery.season = { $in: seasons };  // Season is the same for both languages
     }
 
     // Get all recipes matching base filters

src/routes/api/rezepte/search/+server.ts

@@ -5,36 +5,49 @@ import { dbConnect } from '../../../../utils/db';
 
 export const GET: RequestHandler = async ({ url, locals }) => {
   await dbConnect();
-  
+
   const query = url.searchParams.get('q')?.toLowerCase().trim() || '';
   const category = url.searchParams.get('category');
-  const tag = url.searchParams.get('tag');
+
+  // Support both single tag (backwards compat) and multiple tags
+  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');
+
+  // Support both single season (backwards compat) and multiple seasons
+  const singleSeason = url.searchParams.get('season');
+  const multipleSeasons = url.searchParams.get('seasons');
+  const seasons = multipleSeasons
+    ? multipleSeasons.split(',').map(s => parseInt(s.trim())).filter(n => !isNaN(n))
+    : (singleSeason ? [parseInt(singleSeason)].filter(n => !isNaN(n)) : []);
+
   const favoritesOnly = url.searchParams.get('favorites') === 'true';
-  
+
   try {
     // Build base query
     let dbQuery: any = {};
-    
+
     // Apply filters based on context
     if (category) {
       dbQuery.category = category;
     }
-    
-    if (tag) {
-      dbQuery.tags = { $in: [tag] };
+
+    // Multi-tag AND logic: recipe must have ALL selected tags
+    if (tags.length > 0) {
+      dbQuery.tags = { $all: tags };
     }
-    
+
     if (icon) {
       dbQuery.icon = icon;
     }
-    
-    if (season) {
-      const seasonNum = parseInt(season);
-      if (!isNaN(seasonNum)) {
-        dbQuery.season = { $in: [seasonNum] };
-      }
+
+    // Multi-season OR logic: recipe in any selected season
+    if (seasons.length > 0) {
+      dbQuery.season = { $in: seasons };
     }
     
     // Get all recipes matching base filters