fix: fixed user creation and channel creation

back/api/channels.js

@@ -70,6 +70,17 @@ router.post('/add', async (req, res) => {
         return res.status(401).send({ error: 'Invalid token' });
     }
 
+    const channel = await getChannel(connection, name);
+    if (channel[0]) {
+        connection.end();
+        return res.status(400).send({ error: 'Channel already exists' });
+    }
+
+    if (!/^[a-zA-Z0-9-_]+$/.test(name)) {
+        connection.end();
+        return res.status(400).send({ error: 'Invalid channel name' });
+    }
+
     await addChannel(connection, name, description);
     connection.end();
     res.send({ message: 'Channel added' });