refactor(font): absorb FetchFontsByIds store into Font entity

FetchFontsByIds was data-access for the Font aggregate wearing a feature
costume: a single FontsByIdsStore (BaseQueryStore over Font's proxy API),
no UI, consumed only by comparisonStore. Move it beside fontCatalogStore
in the Font entity, collapse its deep $entities/Font imports to relative
paths, expose via the Font public API, and delete the feature slice.

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

@@ -15,13 +15,13 @@
 
 import {
     type FontLoadRequestConfig,
+    FontsByIdsStore,
     type UnifiedFont,
     fontCatalogStore,
     fontLifecycleManager,
     getFontUrl,
 } from '$entities/Font';
 import { typographySettingsStore } from '$features/AdjustTypography/model';
-import { FontsByIdsStore } from '$features/FetchFontsByIds';
 import { createPersistentStore } from '$shared/lib';
 import { untrack } from 'svelte';
 import { getPretextFontString } from '../../lib';