Add qualified efficiency leaderboard rankings

docs/leaderboard.md

@@ -72,6 +72,21 @@ player-rounds: four players progressing from game start to round 8 contribute 28
 Highest-round records always use the round reached in a completed match,
 including the final round and players who joined mid-game.
 
+Efficiency rankings are also available for **Headshots / kills**, **Kills per
+down**, **Average kills**, **Average rounds**, and **Completion rate**. Each
+requires at least five completed games in the selected game/map scope. Headshot
+rate also requires 100 kills; kills per down requires five downs. The board shows
+the numerator, denominator and game count beside each ratio. Ratios are computed
+from aggregate counters, not an average of individual match percentages.
+Completion rate is the share of those ended games whose final report contained
+the player; it is not a win rate. Active and interrupted games do not enter any
+denominator. Zero-denominator ratios remain unknown and are not ranked.
+
+Qualification is applied before ranking, search and pagination. Summary cards
+still describe all players in the game/map selection, including those below the
+threshold. Profile metrics show their values and whether the player qualifies
+for the combined lifetime board; a scoped board can have a smaller sample.
+
 Round totals require the player to appear in consecutive observations. If a
 report omits them, their return starts a new participation interval and the gap
 is not credited. The payload cannot tell whether a present player was alive,
@@ -124,4 +139,7 @@ identity. Both `total` and `summary.players` count unique GUIDs; only `total` is
 limited by the player search.
 
 Metric keys are `highestRound`, `kills`, `roundsSurvived`, `headshots`, `revives`,
-`downs`, `gamesPlayed`, `gamesCompleted`, `bestKills`, and `bestScore`.
+`downs`, `gamesPlayed`, `gamesCompleted`, `bestKills`, `bestScore`, `headshotRate`,
+`killsPerDown`, `averageKills`, `averageRounds`, and `completionRate`.
+Efficiency values in entries are unrounded ratios (for example, `0.5` means 50%)
+or `null` when their denominator is zero. UI percentages multiply by 100.