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

Backend/scripts/migrate-better-auth.ts

@@ -0,0 +1,47 @@
+import { and, eq } from 'drizzle-orm';
+
+import { db } from '../db/client';
+import { accounts, users } from '../db/schema';
+
+const PROVIDER_ID = 'credential';
+
+const run = async (): Promise<void> => {
+  const existingUsers = await db.select({
+    id: users.id,
+    passwordHash: users.passwordHash,
+  }).from(users);
+
+  let created = 0;
+
+  for (const user of existingUsers) {
+    const account = await db.query.accounts.findFirst({
+      where: and(
+        eq(accounts.userId, user.id),
+        eq(accounts.providerId, PROVIDER_ID),
+        eq(accounts.accountId, user.id),
+      ),
+    });
+
+    if (account) {
+      continue;
+    }
+
+    await db.insert(accounts).values({
+      userId: user.id,
+      accountId: user.id,
+      providerId: PROVIDER_ID,
+      password: user.passwordHash,
+    });
+
+    created += 1;
+  }
+
+  console.log(`Created ${created} credential account(s).`);
+};
+
+run()
+  .then(() => process.exit(0))
+  .catch((error) => {
+    console.error('Failed to migrate Better Auth accounts', error);
+    process.exit(1);
+  });