fix: default admin user to 'lab', case-insensitive OS detection for iSCSI

- Firstboot script defaults admin user to 'lab' instead of bastion's
  config.adminUser (which was 'michal' from host system)
- iSCSI OS detection uses case-insensitive match for 'fedora'

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bastion/src/modules/modules/k3s/src/operations/iscsi.ts

@@ -13,7 +13,8 @@ export const enableIscsi: Operation = async (ctx): Promise<OperationResult> => {
 
   // Install the package (detect distro)
   const osRelease = await ctx.ssh.exec("cat /etc/os-release", sshOpts(ctx));
-  const isFedora = osRelease.stdout.includes("fedora") || osRelease.stdout.includes("rhel") || osRelease.stdout.includes("centos");
+  const osLower = osRelease.stdout.toLowerCase();
+  const isFedora = osLower.includes("fedora") || osLower.includes("rhel") || osLower.includes("centos");
 
   const pkg = isFedora ? "iscsi-initiator-utils" : "open-iscsi";
   const installCmd = isFedora ? `dnf install -y ${pkg}` : `apt-get install -y ${pkg}`;