Refactor Vite configuration and add environment type definitions

- Removed local Vite config file
- Updated dev scripts to use default config
- Added env.d.ts for type definitions
- Enhanced Vite config with dynamic proxy
- Simplified build and dev script commands

lightrag_webui/src/env.d.ts

@@ -0,0 +1,7 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_API_PROXY: string
+  readonly VITE_API_ENDPOINTS: string
+  readonly VITE_BACKEND_URL: string
+}