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>

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

@@ -1,4 +1,4 @@
-import { filterManager } from '$features/GetFonts';
+import { appliedFilterStore } from '$features/GetFonts';
 import {
     render,
     screen,
@@ -7,7 +7,7 @@ import Search from './Search.svelte';
 
 describe('Search', () => {
     beforeEach(() => {
-        filterManager.queryValue = '';
+        appliedFilterStore.queryValue = '';
     });
 
     describe('Rendering', () => {
@@ -23,8 +23,8 @@ describe('Search', () => {
     });
 
     describe('Value binding', () => {
-        it('reflects filterManager.queryValue as initial value', () => {
-            filterManager.queryValue = 'Inter';
+        it('reflects appliedFilterStore.queryValue as initial value', () => {
+            appliedFilterStore.queryValue = 'Inter';
             render(Search);
             expect(screen.getByRole('textbox')).toHaveValue('Inter');
         });