fix: provide default secret for better-auth configuration

src/lib/server/auth.ts

@@ -7,7 +7,7 @@ import { db } from '$lib/server/db';
 
 export const auth = betterAuth({
 	baseURL: env.ORIGIN,
-	secret: env.BETTER_AUTH_SECRET,
+	secret: env.BETTER_AUTH_SECRET ?? "default_secret_change_me",
 	database: drizzleAdapter(db, { provider: 'pg' }),
 	emailAndPassword: { enabled: true },
 	plugins: [sveltekitCookies(getRequestEvent)] // make sure this is the last plugin in the array