Replace instance metrics with map lobby counts (Refs #139)

docs/guides/metrics.md

@@ -73,16 +73,23 @@ the same figures for comparison and assistive technology. Zero captured time is
 distinct from an observed empty lobby. Short durations use seconds or minutes so
 a real observation is not rounded to zero.
 
-Map and instance tables support numeric sorting and local search. The map table's
+The map table supports numeric sorting and local search. **Lobbies (avg · peak)**
+shows the time-weighted average and peak concurrent lobby count for each recorded
+game/map pair, with empty lobby-hours beneath. Sort this column by average count.
+The average divides all captured lobby-hours, including unknown occupancy, by
+that map's captured wall time; collection gaps and periods without recorded lobbies
+for that map are excluded. Peak is the largest captured concurrent count, not the
+number of distinct lobby names. Empty lobby-hours sum time with zero reported
+players across the map's lobbies. Unknown occupancy is not counted as empty;
+empty time is unavailable when no occupancy is known. Lobby counts are unavailable
+without captured time. Per-lobby match and activity history is available on server pages.
+
+The map table's
 **No empty lobby** column uses occupancy alone and retains the known map-time
 denominator in its details. Unknown map availability stays distinct from zero
 time without a spare. Evidence can be limited by short observations or unknown
 occupancy, never by missing player limits.
 
-Instance rows describe history grouped by server name, which can include different
-instances if a name was reused. **Open current server** appears only when that name
-is currently registered; its destination represents the current registration.
-
 ## Comparisons and activity
 
 Previous-period comparisons use the preceding equally long window with identical