fix(auth): address Task 13 deployment review findings

backend/src/server.ts

@@ -1,5 +1,6 @@
 import { buildApp, type AppWithAuthSessionStore } from "./app.js";
 import { loadConfig } from "./config.js";
+import { formatStartupFailure } from "./startup-error.js";
 const config = loadConfig(process.env);
 const app = buildApp(config) as AppWithAuthSessionStore;
 
@@ -17,7 +18,7 @@ async function start(): Promise<void> {
   console.log(`backend listening on ${address}`);
 }
 
-void start().catch(() => {
-  console.error("backend startup failed");
+void start().catch((error: unknown) => {
+  console.error(formatStartupFailure(error));
   process.exitCode = 1;
 });