refactor: rename firebaseAuthStore to authStore with shared test fixtures (#10483)

## Summary

Rename `useFirebaseAuthStore` → `useAuthStore` and
`FirebaseAuthStoreError` → `AuthStoreError`. Introduce shared mock
factory (`authStoreMock.ts`) to replace 16 independent bespoke mocks.

## Changes

- **What**: Mechanical rename of store, composable, class, and store ID
(`firebaseAuth` → `auth`). Created
`src/stores/__tests__/authStoreMock.ts` — a shared mock factory with
reactive controls, used by all consuming test files. Migrated all 16
test files from ad-hoc mocks to the shared factory.
- **Files**: 62 files changed (rename propagation + new test infra)

## Review Focus

- Mock factory API design in `authStoreMock.ts` — covers all store
properties with reactive `controls` for per-test customization
- Self-test in `authStoreMock.test.ts` validates computed reactivity

Fixes #8219

## Stack

This is PR 1/5 in a stacked refactoring series:
1. **→ This PR**: Rename + shared test fixtures
2. #10484: Extract auth-routing from workspaceApi
3. #10485: Auth token priority tests
4. #10486: Decompose MembersPanelContent
5. #10487: Consolidate SubscriptionTier type

---------

Co-authored-by: Alexander Brown <drjkl@comfy.org>

src/platform/cloud/subscription/components/PricingTable.test.ts

@@ -31,8 +31,8 @@ vi.mock('@/platform/cloud/subscription/composables/useSubscription', () => ({
   })
 }))
 
-vi.mock('@/composables/auth/useFirebaseAuthActions', () => ({
-  useFirebaseAuthActions: () => ({
+vi.mock('@/composables/auth/useAuthActions', () => ({
+  useAuthActions: () => ({
     accessBillingPortal: mockAccessBillingPortal,
     reportError: mockReportError
   })
@@ -56,13 +56,13 @@ vi.mock('@/composables/useErrorHandling', () => ({
   })
 }))
 
-vi.mock('@/stores/firebaseAuthStore', () => ({
-  useFirebaseAuthStore: () =>
+vi.mock('@/stores/authStore', () => ({
+  useAuthStore: () =>
     reactive({
       getAuthHeader: mockGetAuthHeader,
       userId: computed(() => mockUserId.value)
     }),
-  FirebaseAuthStoreError: class extends Error {}
+  AuthStoreError: class extends Error {}
 }))
 
 vi.mock('@/platform/telemetry', () => ({