refactor(entities/Font): named public API and expose stores via root barrel

Stores were only reachable by deep-importing $entities/Font/model, so
consumers reached past the slice public API (FSD anti-pattern D, B-3/D-2).

- convert the Font barrels (root, model, model/store, model/types) to
  explicit named exports with export/export type split (B-1)
- re-export the lazy store accessors/classes from the root barrel so the
  entity public API is complete and inert at import (construction stays
  lazy; the root already loads tanstack via ./ui)
- repoint all consumers (SampleList, SampleListSection, FontList,
  comparisonStore, bindings) from $entities/Font/model to $entities/Font

src/widgets/ComparisonView/model/stores/comparisonStore.svelte.ts

@@ -13,18 +13,16 @@
  * - Slider position for character-by-character morphing
  */
 
-import {
-    type FontLoadRequestConfig,
-    type UnifiedFont,
-    getFontUrl,
-} from '$entities/Font';
 import {
     type FontCatalogStore,
     type FontLifecycleManager,
+    type FontLoadRequestConfig,
     FontsByIdsStore,
+    type UnifiedFont,
     getFontCatalog,
     getFontLifecycleManager,
-} from '$entities/Font/model';
+    getFontUrl,
+} from '$entities/Font';
 import {
     type TypographySettingsStore,
     getTypographySettingsStore,