feat: add graceful degradation and conditional favorites filter

Add progressive enhancement to hide filter panel when JavaScript is
disabled, and conditionally render favorites filter based on login status.

Search Component:
- Added showFilters state (default false)
- Set showFilters to true in onMount when JS is enabled
- Wrapped FilterPanel in {#if showFilters} for graceful degradation
- Filters hidden without JavaScript, visible with JS

FilterPanel:
- Split grid layout into two variants:
  - with-favorites: 5 columns (120px 120px 1fr 160px 90px)
  - without-favorites: 4 columns (120px 120px 1fr 160px)
- Conditionally render FavoritesFilter only when isLoggedIn
- Apply appropriate class based on login status

FavoritesFilter:
- Simplified template (no internal login check)
- Only rendered when user is logged in via FilterPanel

UX:
- Non-JS browsers: Simple search only, filters gracefully hidden
- Not logged in: 4-column layout without favorites filter
- Logged in: 5-column layout with favorites filter

src/lib/components/Search.svelte

@@ -27,6 +27,7 @@
     });
 
     let searchQuery = $state('');
+    let showFilters = $state(false);
 
     // Filter data loaded from APIs
     let availableTags = $state([]);
@@ -246,6 +247,9 @@
             clearButton.style.display = 'flex';
         }
 
+        // Enable filter panel for JS-enabled browsers
+        showFilters = true;
+
         // Get initial search value from URL if present
         const urlParams = new URLSearchParams(window.location.search);
         const urlQuery = urlParams.get('q');
@@ -340,20 +344,22 @@ scale: 0.8 0.8;
   </button>
 </form>
 
-<FilterPanel
-  availableCategories={categories}
-  {availableTags}
-  {availableIcons}
-  {selectedCategory}
-  {selectedTags}
-  {selectedIcon}
-  {selectedSeasons}
-  {selectedFavoritesOnly}
-  {lang}
-  {isLoggedIn}
-  onCategoryChange={handleCategoryChange}
-  onTagToggle={handleTagToggle}
-  onIconChange={handleIconChange}
-  onSeasonChange={handleSeasonChange}
-  onFavoritesToggle={handleFavoritesToggle}
-/>
+{#if showFilters}
+  <FilterPanel
+    availableCategories={categories}
+    {availableTags}
+    {availableIcons}
+    {selectedCategory}
+    {selectedTags}
+    {selectedIcon}
+    {selectedSeasons}
+    {selectedFavoritesOnly}
+    {lang}
+    {isLoggedIn}
+    onCategoryChange={handleCategoryChange}
+    onTagToggle={handleTagToggle}
+    onIconChange={handleIconChange}
+    onSeasonChange={handleSeasonChange}
+    onFavoritesToggle={handleFavoritesToggle}
+  />
+{/if}