Core/Arenas: implement arena gameplay for solo player with bots

- player can now hire 1 (2v2) or 2 bots (3v3) gameplay in arenas.
- enemy team will have only bots
- the system should support also 2players vs 2 bots or 3 players vs 3 bots.
- not all arenas might be enabled. this is still WIP
- enemy team bots currently just wait at their spawn point - still WIP

sql/updates/characters/master/2026_07_19_00_characters.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `character_arena_stats`
+ADD COLUMN `rating` smallint unsigned NOT NULL DEFAULT '0' AFTER `matchMakerRating`;