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/onboarding/CloudAuthTimeoutView.vue

@@ -74,7 +74,7 @@ import { ref } from 'vue'
 import { useRouter } from 'vue-router'
 
 import Button from '@/components/ui/button/Button.vue'
-import { useFirebaseAuthActions } from '@/composables/auth/useFirebaseAuthActions'
+import { useAuthActions } from '@/composables/auth/useAuthActions'
 
 interface Props {
   errorMessage?: string
@@ -83,7 +83,7 @@ interface Props {
 defineProps<Props>()
 
 const router = useRouter()
-const { logout } = useFirebaseAuthActions()
+const { logout } = useAuthActions()
 const showTechnicalDetails = ref(false)
 
 const handleRestart = async () => {