Playtime from PlaytimeHistory's database (SAW_PT_DSN)

A public Playtime tab and player-drawer playtime, and staff-only figures
(who's on, staff activity, disconnect reasons, countries, names, sessions)
for @css/generic on the staff panel and on the public site when signed in.
Hidden unless SAW_PT_DSN is set and its tables are there.

internal/web/assets/admin.html

@@ -56,6 +56,7 @@
   <div id="toast-root" aria-live="polite"></div>
 
   <script src="/static/common.js"></script>
+  <script src="/static/playtime.js"></script>
   <script src="/static/admin.js"></script>
 </body>
 </html>