Update API target and port configuration; upgrade OpenAI model version

- Changed API proxy target from localhost:5000 to localhost:5500 in both webpack configurations.
- Updated server port from 5000 to 5500 in src/index.js for consistency.
- Upgraded OpenAI model from "gpt-4o-mini" to "gpt-5-mini" in document processing routes, enhancing processing capabilities.

webpack.config.js

@@ -75,7 +75,7 @@ module.exports = {
     },
     proxy: {
       '/api': {
-        target: 'http://localhost:5000',
+        target: 'http://localhost:5500',
         changeOrigin: true,
       },
     },