refactor: extract magic constants — wave 2 (TanStack Query defaults)

Promote the duplicated query lifecycle constants in \$shared/api/queryClient.ts:

- staleTime (5 minutes) -> DEFAULT_QUERY_STALE_TIME_MS
- gcTime (10 minutes)   -> DEFAULT_QUERY_GC_TIME_MS
- retry (3)             -> QUERY_RETRY_COUNT
- retryDelay (1s base, 30s cap) -> QUERY_RETRY_BASE_DELAY_MS + QUERY_RETRY_MAX_DELAY_MS

fontCatalogStore and availableFilterStore now import the stale/gc
constants instead of re-deriving '5 * 60 * 1000' / '10 * 60 * 1000'.

fontCatalogStore.svelte.spec.ts's queryClient mock now passes through
the new named exports via importOriginal so the consumer's imports
resolve.

src/shared/api/queryClient.ts

@@ -1,5 +1,31 @@
 import { QueryClient } from '@tanstack/query-core';
 
+/**
+ * Data remains fresh for this long after fetch. Stores that override
+ * staleness (e.g. filtered queries) can use 0 to bypass.
+ */
+export const DEFAULT_QUERY_STALE_TIME_MS = 5 * 60 * 1000;
+
+/**
+ * Unused cache entries are garbage collected after this long.
+ */
+export const DEFAULT_QUERY_GC_TIME_MS = 10 * 60 * 1000;
+
+/**
+ * How many times a failed query is retried before surfacing the error.
+ */
+export const QUERY_RETRY_COUNT = 3;
+
+/**
+ * Base delay for exponential retry backoff.
+ */
+export const QUERY_RETRY_BASE_DELAY_MS = 1000;
+
+/**
+ * Upper bound on retry delay regardless of attempt index.
+ */
+export const QUERY_RETRY_MAX_DELAY_MS = 30000;
+
 /**
  * TanStack Query client instance
  *
@@ -15,14 +41,8 @@ import { QueryClient } from '@tanstack/query-core';
 export const queryClient = new QueryClient({
     defaultOptions: {
         queries: {
-            /**
-             * Data remains fresh for 5 minutes after fetch
-             */
-            staleTime: 5 * 60 * 1000,
-            /**
-             * Unused cache entries are removed after 10 minutes
-             */
-            gcTime: 10 * 60 * 1000,
+            staleTime: DEFAULT_QUERY_STALE_TIME_MS,
+            gcTime: DEFAULT_QUERY_GC_TIME_MS,
             /**
              * Don't refetch when window regains focus
              */
@@ -31,15 +51,12 @@ export const queryClient = new QueryClient({
              * Refetch on mount if data is stale
              */
             refetchOnMount: true,
+            retry: QUERY_RETRY_COUNT,
             /**
-             * Retry failed requests up to 3 times
+             * Exponential backoff: 1s, 2s, 4s, 8s... capped at 30s
              */
-            retry: 3,
-            /**
-             * Exponential backoff for retries
-             * 1s, 2s, 4s, 8s... capped at 30s
-             */
-            retryDelay: attemptIndex => Math.min(1000 * 2 ** attemptIndex, 30000),
+            retryDelay: attemptIndex =>
+                Math.min(QUERY_RETRY_BASE_DELAY_MS * 2 ** attemptIndex, QUERY_RETRY_MAX_DELAY_MS),
         },
     },
 });