feat: refactor ComparisonStore to use BatchFontStore

Replace hand-rolled async fetching (fetchFontsByIds + isRestoring flag)
with BatchFontStore backed by TanStack Query. Three reactive effects
handle batch sync, CSS font loading, and default-font fallback.
isLoading now derives from batchStore.isLoading + fontsReady.

src/entities/Font/model/store/index.ts

@@ -1,6 +1,9 @@
 // Applied fonts manager
 export { appliedFontsManager } from './appliedFontsStore/appliedFontsStore.svelte';
 
+// Batch font store
+export { BatchFontStore } from './batchFontStore.svelte';
+
 // Single FontStore
 export {
     createFontStore,