fix: prisma url in schema + first user becomes ADMIN

- Add url = env("DATABASE_URL") back to schema (required by Prisma 7.5)
- Simplify prisma.config.ts
- First registered user auto-promoted to ADMIN via databaseHooks
- Subsequent users get HOST role

src/lib/auth.ts

@@ -43,4 +43,27 @@ export const auth = betterAuth({
     expiresIn: 60 * 60 * 24 * 7, // 7 days
     updateAge: 60 * 60 * 24, // 1 day
   },
+  user: {
+    additionalFields: {
+      role: {
+        type: "string",
+        defaultValue: "HOST",
+        input: false,
+      },
+    },
+  },
+  databaseHooks: {
+    user: {
+      create: {
+        before: async (user) => {
+          // Первый зарегистрированный пользователь → ADMIN
+          const count = await prisma.user.count();
+          if (count === 0) {
+            return { data: { ...user, role: "ADMIN" } };
+          }
+          return { data: { ...user, role: "HOST" } };
+        },
+      },
+    },
+  },
 });