simplify per-game table: tracked player only, no rating diff column

Reworked the per-game row layout to be relative to the tracked player
instead of white/black: the tracked player's name+accuracy+rating are
always shown first, the opponent's rating+accuracy (no name) always
second, regardless of which color each side played in a given game -
this keeps columns aligned across rows even as the tracked player
switches sides. Dropped the rating-change-per-game column added
earlier; it pushed the line past mobile width limits.

LichessWebServices/stats_service.py

@@ -583,13 +583,6 @@ class StatsService:
         else:
             tracked_is_white = None
 
-        if tracked_is_white is True:
-            tracked_rating_diff = white.get('ratingDiff')
-        elif tracked_is_white is False:
-            tracked_rating_diff = black.get('ratingDiff')
-        else:
-            tracked_rating_diff = None
-
         return GameRow(
             white_name=white_name,
             black_name=black_name,
@@ -599,8 +592,7 @@ class StatsService:
             black_accuracy=(black.get('analysis') or {}).get('accuracy'),
             result=result,
             created_at=game.get('createdAt', 0),
-            tracked_is_white=tracked_is_white,
-            tracked_rating_diff=tracked_rating_diff
+            tracked_is_white=tracked_is_white
         )
 
     def _process_games_of_period(self, games: List[Dict[str, Any]], username: str, include_games: bool = False) -> GamesOfPeriodStats: