Add foundational API client, UI components, and state management setup

- Created `generate-api-client.sh` for OpenAPI-based TypeScript client generation.
- Added `src/lib/api` with Axios-based API client, error handling utilities, and placeholder for generated types.
- Implemented Zustand-based `authStore` for user authentication and token management.
- Integrated reusable UI components (e.g., `Dialog`, `Select`, `Textarea`, `Sheet`, `Separator`, `Checkbox`) using Radix UI and utility functions.
- Established groundwork for client-server integration, state management, and modular UI development.

frontend/src/config/index.ts

@@ -0,0 +1,27 @@
+// Application configuration
+// Environment variables, constants, feature flags, etc.
+
+export const config = {
+  api: {
+    baseUrl: process.env.NEXT_PUBLIC_API_URL || 'http://localhost:8000/api/v1',
+    timeout: parseInt(process.env.NEXT_PUBLIC_API_TIMEOUT || '30000', 10),
+  },
+  app: {
+    name: process.env.NEXT_PUBLIC_APP_NAME || 'Template Project',
+    url: process.env.NEXT_PUBLIC_APP_URL || 'http://localhost:3000',
+  },
+  auth: {
+    tokenRefreshThreshold: parseInt(process.env.NEXT_PUBLIC_TOKEN_REFRESH_THRESHOLD || '300000', 10),
+    accessTokenExpiry: parseInt(process.env.NEXT_PUBLIC_ACCESS_TOKEN_EXPIRY || '900000', 10),
+    refreshTokenExpiry: parseInt(process.env.NEXT_PUBLIC_REFRESH_TOKEN_EXPIRY || '604800000', 10),
+  },
+  features: {
+    enableRegistration: process.env.NEXT_PUBLIC_ENABLE_REGISTRATION === 'true',
+    enableSessionManagement: process.env.NEXT_PUBLIC_ENABLE_SESSION_MANAGEMENT === 'true',
+  },
+  debug: {
+    api: process.env.NEXT_PUBLIC_DEBUG_API === 'true',
+  },
+} as const;
+
+export type AppConfig = typeof config;