Improve metrics clarity, exploration, and refresh reliability

docs/metrics.md

@@ -3,6 +3,28 @@
 Metrics is a primary navigation tab at `/metrics` (keyboard shortcut: `g m`).
 Choose the past 24 hours, 7 days, or 30 days. The page refreshes every minute.
 
+The overview shows **Time with players** (occupied server-hours divided by known
+server-hours) and **Player-hours**. Known and unknown status time remain visible
+alongside the totals. **Last collected** is the newest recorded batch, including
+unknown checks; **Report refreshed** is when this report was calculated. Collection
+stops when no servers are registered. Earliest retained observations do not prove
+continuous history or the original installation date.
+
+Background refresh keeps the last successful report visible on failure and offers
+Retry. Returning to a visible tab refreshes immediately. The selected range is
+stored in the URL, and refreshes preserve table controls and chart selection.
+
+The timeline has labelled axes and marks partial edge periods. Select a period,
+use Previous/Next, or select a bar to inspect its exact interval and values. The
+time table supplies the same figures for comparison and assistive technology.
+Zero captured time is distinct from an observed empty server. Short durations use
+seconds or minutes so a real observation is not rounded to zero.
+
+Map and server tables support numeric sorting and local search. Their searches
+apply only to the named table. Known-capacity duration stays next to all-full time.
+Server identities retain the technical name; rows describe history grouped by
+name, which may include different instances if a name was reused.
+
 - Utilized means a successful status response reported at least one player.
 - Idle means a successful response reported zero players.
 - Unknown covers failed checks, provisioning, and unavailable containers; it is excluded from utilization percentages.