Refactor API structure and integrate new modular API client

- Replaced legacy apiService with a new modular api client structure.
- Updated AuthContext, OAuthButtons, and AuthCallbackPage to use the new api client.
- Created separate services for auth, sounds, playlists, and users.
- Implemented centralized API configuration and error handling.
- Added support for OAuth providers and token exchange.
- Introduced a Toaster component for notifications in App.
- Updated API endpoints and request handling for better maintainability.

src/lib/api/config.ts

@@ -0,0 +1,44 @@
+// API Configuration
+export const API_CONFIG = {
+  BASE_URL: import.meta.env.VITE_API_BASE_URL || 'http://localhost:8000',
+  TIMEOUT: 30000, // 30 seconds
+  RETRY_ATTEMPTS: 1,
+  
+  // API Endpoints
+  ENDPOINTS: {
+    AUTH: {
+      LOGIN: '/api/v1/auth/login',
+      REGISTER: '/api/v1/auth/register',
+      LOGOUT: '/api/v1/auth/logout',
+      REFRESH: '/api/v1/auth/refresh',
+      ME: '/api/v1/auth/me',
+      PROVIDERS: '/api/v1/auth/providers',
+      OAUTH_AUTHORIZE: (provider: string) => `/api/v1/auth/${provider}/authorize`,
+      OAUTH_CALLBACK: (provider: string) => `/api/v1/auth/${provider}/callback`,
+      EXCHANGE_OAUTH_TOKEN: '/api/v1/auth/exchange-oauth-token',
+    },
+    SOUNDS: {
+      LIST: '/api/v1/sounds',
+      CREATE: '/api/v1/sounds',
+      GET: (id: string | number) => `/api/v1/sounds/${id}`,
+      UPDATE: (id: string | number) => `/api/v1/sounds/${id}`,
+      DELETE: (id: string | number) => `/api/v1/sounds/${id}`,
+      UPLOAD: '/api/v1/sounds/upload',
+    },
+    PLAYLISTS: {
+      LIST: '/api/v1/playlists',
+      CREATE: '/api/v1/playlists',
+      GET: (id: string | number) => `/api/v1/playlists/${id}`,
+      UPDATE: (id: string | number) => `/api/v1/playlists/${id}`,
+      DELETE: (id: string | number) => `/api/v1/playlists/${id}`,
+    },
+    USERS: {
+      LIST: '/api/v1/users',
+      GET: (id: string | number) => `/api/v1/users/${id}`,
+      UPDATE: (id: string | number) => `/api/v1/users/${id}`,
+      DELETE: (id: string | number) => `/api/v1/users/${id}`,
+    },
+  },
+} as const
+
+export type ApiEndpoints = typeof API_CONFIG.ENDPOINTS