fix: error handling

- Remove unnecessary try-catch block in createSession function
- Add error handling for missing session ID in socket.js
- Improve error handling in connectDB function
- Add error handling middleware for server errors
- Add default export for get function in env.js

Signed-off-by: wancat <wancat@wancat.cc>

server/src/middleware/error.js

@@ -0,0 +1,5 @@
+// eslint-disable-next-line no-unused-vars
+export default function errorHandler(err, req, res, next) {
+  console.error(err.stack) // Log error stack trace to the console
+  res.status(500).send({ message: err.message }) // Send error response
+}