refactor(font): keep @tanstack out of the entity public API barrel

Extract NonRetryableError into its own tanstack-free module and drop the
./api re-export from the Font slice barrel. Importing $entities/Font no
longer transitively loads @tanstack/query-core or constructs the QueryClient
singleton via the ./api and ./lib (errors) chains — light consumers (domain,
types, consts) and unit specs stop paying for TanStack.

Note: ./ui still pulls the stores; addressed separately.

src/entities/Font/index.ts

@@ -1,4 +1,3 @@
-export * from './api';
 export * from './domain';
 export * from './lib';
 export * from './ui';
@@ -8,6 +7,16 @@ export * from './ui';
 export * from './model/const/const';
 export * from './model/types';
 
+/*
+ * `./api` (proxy clients: `fetchProxyFonts`, `seedFontCache`, …) is intentionally
+ * NOT re-exported here. Those clients import `$shared/api/queryClient`, whose
+ * module eval runs `new QueryClient()` and loads `@tanstack/query-core`. Funneling
+ * them through this barrel made every consumer of `$entities/Font` — including
+ * pure-domain and type-only importers — eager-load TanStack and construct the
+ * client (notably in unit specs). Import API clients via the segment:
+ *   import { fetchProxyFonts } from '$entities/Font/api';
+ */
+
 /*
  * Stores (`fontCatalogStore`, `fontLifecycleManager`, `FontsByIdsStore`) are
  * intentionally NOT re-exported here. They instantiate module-level singletons

src/entities/Font/lib/errors/errors.ts

@@ -1,4 +1,4 @@
-import { NonRetryableError } from '$shared/api/queryClient';
+import { NonRetryableError } from '$shared/api/nonRetryableError';
 
 /**
  * Thrown when the network request to the proxy API fails.