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.go

@@ -43,8 +43,9 @@ var DomainNames = map[string]bool{"domain": true, "domains": true}
 
 // AdminNames are usernames that route to the privileged admin console (PRD §6).
 // The route only opens for accounts whose name is in the operator allowlist
-// (see IsAdmin); the name itself confers nothing.
-var AdminNames = map[string]bool{"admin": true, "sysop": true}
+// (see IsAdmin); the name itself confers nothing — so "root" is just a familiar
+// alias here, not a backdoor.
+var AdminNames = map[string]bool{"admin": true, "sysop": true, "root": true}
 
 // TorURLNames route to the one-shot "fetch a URL over Tor" command (premium).
 var TorURLNames = map[string]bool{"tor-url": true}