refactor: apply clippy let-chains and harden password validation

- Auto-fix 29 clippy warnings by converting nested if-lets to let-chains
- Harden password strength validator to reject restricted substrings
- Simplify rate_limiter state checks using is_none_or
- Improves idiomatic Rust style and overall security posture

src/identity/roles.rs

@@ -191,11 +191,9 @@ pub async fn update_role(
         .find_by_name(name)
         .await
         .map_err(AppError::Database)?
-    {
-        if other.id != id {
+        && other.id != id {
             return Err(AppError::Conflict(format!("role '{name}' already exists")));
         }
-    }
 
     provider
         .roles()