feat(pods/admin): root admin alias, default-caps cleanup, pod rebuild script

- auth: add `root` as an admin-console route alias (alongside admin/sysop);
  still gated by $AGENTBBS_ADMINS — the name confers nothing on its own.
- pods: drop the now-redundant tuneApt apt-sandbox hack. Rootless podman keeps
  its default capability set, so apt/chown/su work without disabling the
  download sandbox.
- scripts/rebuild-pods.sh: recreate all member pods (keeps home volumes) so
  they pick up the current container profile on next `ssh pod@`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/auth/auth_test.go

@@ -3,7 +3,7 @@ package auth
 import "testing"
 
 func TestIsAdminName(t *testing.T) {
-	for _, name := range []string{"admin", "ADMIN", "sysop"} {
+	for _, name := range []string{"admin", "ADMIN", "sysop", "root"} {
 		if !IsAdminName(name) {
 			t.Errorf("IsAdminName(%q) = false, want true", name)
 		}