fix(cli): add restart hint after allowed-hostname change

The server builds its hostname allow-set once at startup. When users
add a new hostname via the CLI, the config file is updated but the
running server doesn't reload it. This adds a clear message telling
users to restart the server for the change to take effect.

Fixes #538

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cli/src/commands/allowed-hostname.ts

@@ -26,6 +26,9 @@ export async function addAllowedHostname(host: string, opts: { config?: string }
     p.log.info(`Hostname ${pc.cyan(normalized)} is already allowed.`);
   } else {
     p.log.success(`Added allowed hostname: ${pc.cyan(normalized)}`);
+    p.log.message(
+      pc.dim("Restart the Paperclip server for this change to take effect."),
+    );
   }
 
   if (!(config.server.deploymentMode === "authenticated" && config.server.exposure === "private")) {