fix: Fix undefined query data and add fallback to Fontshare API

- Add gcTime parameter to TanStack Query config
- Add response validation in fetchFn with detailed logging
- Add fallback to Fontshare API when proxy fails
- Add USE_PROXY_API flag for easy switching
- Fix FontVirtualList generic type constraint
- Simplify font registration logic
- Add comprehensive console logging for debugging

Fixes: Query data cannot be undefined error

src/entities/Font/model/store/unifiedFontStore.svelte.ts

@@ -111,11 +111,29 @@ export class UnifiedFontStore extends BaseFontStore<ProxyFontsParams> {
     protected async fetchFn(params: ProxyFontsParams): Promise<UnifiedFont[]> {
         const response = await fetchProxyFonts(params);
 
+        // Validate response structure
+        if (!response) {
+            console.error('[UnifiedFontStore] fetchProxyFonts returned undefined', { params });
+            throw new Error('Proxy API returned undefined response');
+        }
+
+        if (!response.fonts) {
+            console.error('[UnifiedFontStore] response.fonts is undefined', { response });
+            throw new Error('Proxy API response missing fonts array');
+        }
+
+        if (!Array.isArray(response.fonts)) {
+            console.error('[UnifiedFontStore] response.fonts is not an array', {
+                fonts: response.fonts,
+            });
+            throw new Error('Proxy API fonts is not an array');
+        }
+
         // Store pagination metadata separately for derived values
         this.#paginationMetadata = {
-            total: response.total,
-            limit: response.limit,
-            offset: response.offset,
+            total: response.total ?? 0,
+            limit: response.limit ?? this.params.limit ?? 50,
+            offset: response.offset ?? this.params.offset ?? 0,
         };
 
         return response.fonts;