feat: migrate to Better Auth for authentication, update environment variables, and enhance database schema with accounts and sessions

Backend/routes/videos.ts

@@ -46,16 +46,16 @@ router.post('/upload-url', async (req, res) => {
     return;
   }
 
-  const user = req.user;
+  const authSession = req.auth;
 
-  if (!user) {
+  if (!authSession?.user) {
     res.status(401).json({ message: 'Unauthorized' });
     return;
   }
 
   await ensureMinioBucket();
 
-  const objectKey = buildObjectKey(user.userId, parsed.data.fileName, parsed.data.prefix);
+  const objectKey = buildObjectKey(authSession.user.id, parsed.data.fileName, parsed.data.prefix);
   const uploadUrl = await minioClient.presignedPutObject(minioBucket, objectKey, minioPresignedExpirySeconds);
   const now = new Date();
   const expiresAt = new Date(now.getTime() + minioPresignedExpirySeconds * 1000);
@@ -63,7 +63,7 @@ router.post('/upload-url', async (req, res) => {
   const [videoRecord] = await db
     .insert(videos)
     .values({
-      userId: user.userId,
+      userId: authSession.user.id,
       objectKey,
       bucket: minioBucket,
       uploadUrl,