fix(api): mark schema-validation errors as non-retryable

The proxy returned `{fonts: null, total: 0}` for empty results, which
fetchProxyFonts surfaced as a generic Error. fontCatalogStore wrapped it
as FontNetworkError, and TanStack retried 3× with exponential backoff —
pinning the loading skeleton for ~7s before settling on an empty list.

Schema mismatches are deterministic; retrying only delays surfacing the
contract violation.

- shared/api/queryClient: introduce NonRetryableError marker class.
  The default retry handler short-circuits when it sees this so any
  store using the shared client gets fail-fast behavior for free.
- entities/Font/lib/errors: FontResponseError extends NonRetryableError.
- entities/Font/api/proxy/proxyFonts: throw FontResponseError (was a
  bare Error). Document that ProxyFontsResponse.fonts is always an array.
- entities/Font/.../fontCatalogStore.fetchPage: preserve a
  FontResponseError raised lower in the stack instead of re-wrapping
  it as FontNetworkError.
- features/FilterAndSortFonts/api/filters: throw NonRetryableError on
  invalid filters payloads and document the array-never-null contract.

src/entities/Font/api/proxy/proxyFonts.test.ts

@@ -21,6 +21,7 @@ vi.mock('$shared/api/api', () => ({
 import { api } from '$shared/api/api';
 import { queryClient } from '$shared/api/queryClient';
 import { fontKeys } from '$shared/api/queryKeys';
+import { FontResponseError } from '../../lib/errors/errors';
 import {
     fetchFontsByIds,
     fetchProxyFontById,
@@ -86,16 +87,20 @@ describe('proxyFonts', () => {
             expect(calledUrl).toContain('offset=0');
         });
 
-        test('should throw on invalid response (missing fonts array)', async () => {
+        test('should throw FontResponseError on invalid response (missing fonts array)', async () => {
             mockApiGet({ total: 0 });
 
-            await expect(fetchProxyFonts()).rejects.toThrow('Proxy API returned invalid response');
+            await expect(fetchProxyFonts()).rejects.toSatisfy(
+                e => e instanceof FontResponseError && e.field === 'response.fonts',
+            );
         });
 
-        test('should throw on null response data', async () => {
+        test('should throw FontResponseError on null response data', async () => {
             vi.mocked(api.get).mockResolvedValueOnce({ data: null, status: 200 });
 
-            await expect(fetchProxyFonts()).rejects.toThrow('Proxy API returned invalid response');
+            await expect(fetchProxyFonts()).rejects.toSatisfy(
+                e => e instanceof FontResponseError && e.field === 'response',
+            );
         });
     });