Keep when each account was added and when it last signed in

users.created comes back, beside a new last_login, for whoever maintains
the server. A password sign-in, the token link and a request through the
proxy all count, recorded to the hour so the proxy's per-request vouching
is not a write each time. Settings -> Users and ipx user list show both.
The three user queries now share one row mapping.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

docs/history.md

@@ -21,6 +21,12 @@ column drops earlier the same day, and one stray `entry_state` row. The code had
 - `Db::subscribed_feed_ids` had no callers, though its doc said the scanner walked it.
   `Db::subscriber_count` had one caller asking whether it was above zero, which
   `subscriber_counts().contains_key` answers. `Managed.orphaned` was selected and never read.
+- `users.created` came back the same afternoon, with `last_login` beside it. Nothing read it, but
+  when an account was made and when it last signed in is what you want to know when tidying
+  accounts, and it cannot be recovered later. Both existing accounts got their creation times back
+  from the backup taken before the drop, and a last sign-in from their newest session in it.
+  `last_login` is kept to the hour, because the proxy vouches for every request and that would
+  otherwise be a write each time.
 
 ## 2026-09-12 — Cutting what had outlived its reason