refactor: consolidate leaderboard into 4 categories with sorting

Merge highest_elo/most_elo_gained/elo_change into single elo category.
Remove most_kills/most_matches. Add tertiary_value and sort_by/sort_dir
params. Fix ELO query to use first/last delta instead of cross-type SUM.
Add losses to win rate. All columns sortable via backend re-ranking.

Author: Flegma

hasura/metadata/actions.graphql

@@ -342,6 +342,8 @@ type Query {
     limit: Int
     offset: Int
     exclude_tournaments: Boolean
+    sort_by: String
+    sort_dir: String
   ): LeaderboardResponse!
 }
 
@@ -358,6 +360,7 @@ type LeaderboardEntry {
   player_country: String
   value: Float!
   secondary_value: Float
+  tertiary_value: Float
   matches_played: Int
 }