refactor: use constant for minimum password length and API rate limit

Co-authored-by: Copilot <copilot@github.com>

crates/application/src/use_cases/register.rs

@@ -2,12 +2,14 @@ use domain::{errors::DomainError, models::User, value_objects::Email};
 
 use crate::{commands::RegisterCommand, context::AppContext};
 
+const MIN_PASSWORD_LENGTH: usize = 8;
+
 pub async fn execute(ctx: &AppContext, cmd: RegisterCommand) -> Result<(), DomainError> {
     if !ctx.config.allow_registration {
         return Err(DomainError::Unauthorized("Registration is disabled".into()));
     }
 
-    if cmd.password.len() < 8 {
+    if cmd.password.len() < MIN_PASSWORD_LENGTH {
         return Err(DomainError::ValidationError(
             "Password must be at least 8 characters".into(),
         ));
@@ -16,7 +18,9 @@ pub async fn execute(ctx: &AppContext, cmd: RegisterCommand) -> Result<(), Domai
     let email = Email::new(cmd.email)?;
 
     if ctx.user_repository.find_by_email(&email).await?.is_some() {
-        return Err(DomainError::ValidationError("Email already registered".into()));
+        return Err(DomainError::ValidationError(
+            "Email already registered".into(),
+        ));
     }
 
     let hash = ctx.password_hasher.hash(&cmd.password).await?;