refactor(GetFonts): rename filters/filterManager to available/appliedFilterStore

The 'filters' + 'filterManager' pair didn't reveal the schema-vs-selection
split. Rename to reflect the actual roles:

- FiltersStore / filtersStore       → AvailableFilterStore / availableFilterStore
- createFilterManager / FilterManager → createAppliedFilterStore / AppliedFilterStore
- filterManager singleton            → appliedFilterStore
- mapManagerToParams                 → mapAppliedFiltersToParams

Directories and file basenames follow the new singleton names. Public
barrel signature updated; all consumers (Search, FontSearch, Filters,
FilterControls) point at the new identifiers.

src/widgets/ComparisonView/ui/Search/Search.svelte

@@ -1,11 +1,11 @@
 <!--
     Component: Search
     Typeface search input for the comparison view.
-    Writes through filterManager; the global bridge in $features/GetFonts
+    Writes through appliedFilterStore; the global bridge in $features/GetFonts
     propagates the value into fontStore.
 -->
 <script lang="ts">
-import { filterManager } from '$features/GetFonts';
+import { appliedFilterStore } from '$features/GetFonts';
 import { SearchBar } from '$shared/ui';
 </script>
 
@@ -15,7 +15,7 @@ import { SearchBar } from '$shared/ui';
         class="w-full"
         placeholder="Typeface Search"
         aria-label="Search typefaces"
-        bind:value={filterManager.queryValue}
+        bind:value={appliedFilterStore.queryValue}
         fullWidth
     />
 </div>