fix(server): log unhandled rejections instead of crashing the process

Node 24 terminates the whole process on an unhandled promise rejection, so a
single request's stray rejection could take the server down for every user
(as the USER_STOPPED agent-abort bug did). Add a process-level unhandledRejection
handler that logs and keeps serving. Uncaught exceptions are intentionally left
on Node's default crash-and-restart, since process state is unsafe afterward.

Claude-Session: https://claude.ai/code/session_01ULhhLQ24DvnYwzP4afDuye

apps/server/src/index.ts

@@ -10,6 +10,14 @@ export { createApp } from "./http/app";
 async function main() {
 	await runStartupChecks();
 
+	// Safety net: Node 24 crashes the whole process on an unhandled rejection. One request's
+	// stray promise must not take the server down for everyone, so log and keep serving.
+	// Registered after startup checks so a broken startup still fails loudly. (Left uncaught
+	// exceptions on Node's default crash-and-restart, since process state is unsafe after one.)
+	process.on("unhandledRejection", (reason) => {
+		console.error("[unhandledRejection]", reason);
+	});
+
 	const port =
 		process.env.NODE_ENV === "production" ? Number.parseInt(process.env.PORT ?? "3000", 10) : env.SERVER_PORT;