fix(backend): guard against missing BETTER_AUTH_SECRET

Co-authored-by: Ona <no-reply@ona.com>

apps/aelis-backend/src/auth/index.ts

@@ -7,6 +7,10 @@ import type { Database } from "../db/index.ts"
 import * as schema from "../db/schema.ts"
 
 export function createAuth(db: Database) {
+	if (!process.env.BETTER_AUTH_SECRET) {
+		throw new Error("BETTER_AUTH_SECRET is not set")
+	}
+
 	return betterAuth({
 		database: drizzleAdapter(db, {
 			provider: "pg",