feat: user tombstone and retired usernames

crates/bootstrap/tests/http_handlers/support.rs

@@ -227,6 +227,28 @@ impl UserRepository for ErroringUserRepo {
     ) -> Result<(), DomainError> {
         panic!()
     }
+    async fn mark_deleted(
+        &self,
+        _: &UserId,
+        _: &[domain::events::DomainEvent],
+    ) -> Result<(), DomainError> {
+        panic!()
+    }
+    async fn find_tombstoned_by_id(
+        &self,
+        _: &UserId,
+    ) -> Result<Option<domain::models::User>, DomainError> {
+        panic!()
+    }
+    async fn is_username_retired(
+        &self,
+        _: &domain::value_objects::Username,
+    ) -> Result<bool, DomainError> {
+        panic!()
+    }
+    async fn count_active_admins(&self) -> Result<u64, DomainError> {
+        panic!()
+    }
 }
 
 /// Auth stub that accepts any bearer token and resolves it to a fixed user id,