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/shared/api/nonRetryableError.ts

@@ -0,0 +1,14 @@
+/**
+ * Marker base class for errors that retrying will never fix — schema-validation
+ * failures, unauthorized responses, contract violations, etc.
+ *
+ * The queryClient retry handler short-circuits when it sees this; without it,
+ * a non-transient backend bug pins the UI through the full retry budget
+ * (default 3× exponential backoff ≈ 7s).
+ *
+ * Lives in its own module — free of `@tanstack/query-core` — so error types that
+ * extend it (e.g. `FontResponseError`) can be imported without dragging the
+ * TanStack client and its eager `new QueryClient()` instantiation into the
+ * importer's module graph. See the barrel-coupling notes in the FSD audit.
+ */
+export class NonRetryableError extends Error {}