test(ai): answer both switch readers from one source in flag mocks

Eight files mocked `@/lib/feature-flags` with `getAssistantFlags` alone.
The capability loader reads `loadAssistantSwitches`, so wherever it ran
it threw and every capability resolved to `check_failed`. A shared
factory now points both readers at the function the test drives.

Only the config-change chain reached the loader. Its fixture means AI
switched off by the operator; it now supplies the loader's other inputs
and asserts `operator_disabled` on the digest, so a starved loader turns
it red instead of passing on the failure path.

src/app/api/user/ai-provider/__tests__/route.test.ts

@@ -48,9 +48,11 @@ vi.mock("@/lib/ai/server-provider-health", () => ({
   readServerProviderHealth: vi.fn(),
 }));
 
-vi.mock("@/lib/feature-flags", () => ({
-  getAssistantFlags: vi.fn(),
-}));
+vi.mock("@/lib/feature-flags", async () =>
+  (
+    await import("@/__tests__/helpers/assistant-switches-mock")
+  ).mockAssistantSwitches(vi.fn()),
+);
 
 vi.mock("@/lib/sharing/provider-work-authority", () => ({
   providerWorkAuthorityForRecord: vi.fn(() => ({ origin: "owner" })),