refactor: remove dead code and #[allow(dead_code)] annotations

Removed unused sync podman_command/docker_command methods.
Removed dead_code annotations from User and AuthManager (now actively used).

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

core/archipelago/src/auth.rs

@@ -67,7 +67,6 @@ struct OnboardingState {
     complete: bool,
 }
 
-#[allow(dead_code)]
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct User {
     pub password_hash: String,
@@ -80,12 +79,10 @@ pub struct User {
     pub role: UserRole,
 }
 
-#[allow(dead_code)]
 pub struct AuthManager {
     data_dir: PathBuf,
 }
 
-#[allow(dead_code)]
 impl AuthManager {
     pub fn new(data_dir: PathBuf) -> Self {
         Self { data_dir }