Wire plugin services through Bind/InjectFrom and AppContext so HTTP and
workers resolve dependencies after Apply. Register TaskHandler objects
with persisted results, and implement send_email_code, mail:send,
cleanup_inactive_users, and dispatch_bot_msg.
Using2/Using3 flattened per-dependency injection failures with %v while
Using1 wrapped with %w, so errors.Is could not see ErrServiceNotFound
through a multi-dependency resolution failure.