feat: implement type-safe environment configuration and add .env.example files for web and landing apps

apps/web/src/environment/env.ts

@@ -0,0 +1,10 @@
+/**
+ * Type-safe Environment Wrapper for apps/web.
+ * DO NOT use `import.meta.env` directly in components. Import this `ENV` object instead.
+ */
+export const ENV = {
+  API_BASE_URL: import.meta.env.VITE_API_BASE_URL || 'http://localhost:8000/api',
+  APP_ENV: (import.meta.env.VITE_APP_ENV || 'development') as 'development' | 'staging' | 'production',
+  IS_PROD: import.meta.env.VITE_APP_ENV === 'production',
+} as const;
+