fix(web/m7-362): repair Vitest fixtures (matchMedia.fire, listenbrainz mock)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/lib/stores/theme.svelte.test.ts

@@ -20,7 +20,14 @@ function setupMatchMedia(prefersLight: boolean) {
   vi.stubGlobal('window', {
     matchMedia: () => mql
   });
-  return { mql, listeners, fire: (matches: boolean) => listeners.forEach((cb) => cb({ matches })) };
+  return {
+    mql,
+    listeners,
+    fire: (matches: boolean) => {
+      mql.matches = matches;
+      listeners.forEach((cb) => cb({ matches }));
+    }
+  };
 }
 
 beforeEach(() => {

web/src/routes/settings/Appearance.test.ts

@@ -1,16 +1,29 @@
 import { describe, expect, test, vi, beforeEach } from 'vitest';
 import { render, screen, fireEvent } from '@testing-library/svelte';
 
-vi.mock('$lib/api/listenbrainz', () => ({
-  createLBStatusQuery: () => ({
-    subscribe: () => () => {},
-    isPending: false,
-    isError: false,
-    data: { token_set: false, enabled: false }
-  }),
-  createTokenMutation: () => ({ subscribe: () => () => {}, mutate: vi.fn(), isPending: false }),
-  createEnabledMutation: () => ({ subscribe: () => () => {}, mutate: vi.fn(), isPending: false })
-}));
+vi.mock('$lib/api/listenbrainz', () => {
+  // Mocks must look like a Svelte readable store. The page reads e.g.
+  // $status.isPending, which is shorthand for "subscribe to status,
+  // then read .isPending on the emitted value." Returning an object
+  // that ALSO carries isPending/etc. as bare properties (without a
+  // working subscribe) makes $status resolve to undefined.
+  const stub = <T extends Record<string, unknown>>(value: T) => ({
+    subscribe: (run: (v: T) => void) => {
+      run(value);
+      return () => {};
+    }
+  });
+  return {
+    createLBStatusQuery: () =>
+      stub({
+        isPending: false,
+        isError: false,
+        data: { token_set: false, enabled: false }
+      }),
+    createTokenMutation: () => stub({ mutate: vi.fn(), isPending: false }),
+    createEnabledMutation: () => stub({ mutate: vi.fn(), isPending: false })
+  };
+});
 
 vi.mock('@tanstack/svelte-query', async (orig) => {
   const actual = (await orig()) as Record<string, unknown>;