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/features/FilterAndSortFonts/model/store/bindings.svelte.ts

@@ -9,7 +9,7 @@
  * observer, so it lives at module scope, not in any individual widget.
  */
 
-import { getFontCatalog } from '$entities/Font/model';
+import { getFontCatalog } from '$entities/Font';
 import { untrack } from 'svelte';
 import { mapAppliedFiltersToParams } from '../../lib/mapper/mapAppliedFiltersToParams';
 import { mapFilterMetadataToGroups } from '../../lib/mapper/mapFilterMetadataToGroups';