Refactor to enforce AuthContext usage over useAuthStore and improve test stability

- Replaced `useAuthStore` with `useAuth` from `AuthContext` across frontend components and tests to ensure dependency injection compliance.
- Enhanced E2E test stability by delaying navigation until the auth context is fully initialized.
- Updated Playwright configuration to use a single worker to prevent mock conflicts.
- Refactored test setup to consistently inject `AuthProvider` for improved isolation and mocking.
- Adjusted comments and documentation to clarify dependency injection and testability patterns.

frontend/src/lib/auth/AuthContext.tsx

@@ -13,6 +13,7 @@
 
 import { createContext, useContext } from "react";
 import type { ReactNode } from "react";
+// eslint-disable-next-line no-restricted-imports -- This is the DI boundary, needs real store for production
 import { useAuthStore as useAuthStoreImpl } from "@/lib/stores/authStore";
 import type { User } from "@/lib/stores/authStore";