refactor(core): improve typing and test coverage

Restructure database and user CLI commands, make passwords write-only
model properties, and use the UTC datetime constant throughout the
application.

Add PEP 287-style documentation and expand receiver, scanner, sender,
and URL security tests to cover error paths and edge cases.

1 files changed, 7 insertions, 1 deletions

diff --git a/webmentions_ssg/auth.py b/webmentions_ssg/auth.py
index f8fd28c..7bd93a3 100644
--- a/webmentions_ssg/auth.py
+++ b/webmentions_ssg/auth.py
@@ -9,5 +9,11 @@ AUTH.login_view = "root.login"
 
 
 @AUTH.user_loader
-def load_user(id):
+def load_user(id: int) -> User | None:
+    """
+    Load a user from the database by identifier.
+
+    :param id: User identifier stored in the login session.
+    :return: Matching user, or ``None`` if no user exists with the identifier.
+    """
     return db.session.get(User, int(id))