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/utils/env.js

@@ -1,3 +1,4 @@
+/* eslint-disable import/prefer-default-export */
 export function get(key, defaultValue) {
   const value = process.env[key]
   if (value != null) {