fix(users): a password reset signs out every session begun with the old password (#5427)

#5427 "A password reset doesn't end the sessions already signed in with
the old password": users.sessions_since (migration 0038) is set on reset;
refresh_session_user ends a session whose login_at is earlier. An admin
resetting their own password carries on signed in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/templates/settings/user.html

@@ -72,7 +72,7 @@
       <div class="field">
         <label class="field-label" for="u-pw">New password</label>
         <input class="input" id="u-pw" type="password" name="password" minlength="{{ min_password }}" required autocomplete="new-password">
-        <span class="field-hint">At least {{ min_password }} characters. Give it to them yourself; Steward sends no email for it.</span>
+        <span class="field-hint">At least {{ min_password }} characters. Give it to them yourself; Steward sends no email for it. Anywhere they're signed in now, they're signed out.</span>
       </div>
       <div class="field">
         <label class="field-label" for="u-pw2">Again</label>