feat(赛马插件): 调整参与奖励并优化赛马显示对齐

- 将参与奖励从50点降低到20点以平衡经济系统
- 为所有马主添加参与奖励计算和发放逻辑
- 优化赛况显示中的马名对齐，支持中文字符宽度计算

danding_bot/plugins/group_horse_racing/commands.py

@@ -146,6 +146,10 @@ def _describe_points_delta(delta: int) -> str:
 def _build_point_changes(room: Room, odds: dict[str, float]) -> tuple[dict[str, int], dict[str, str]]:
     point_changes: dict[str, int] = {}
 
+    # Participation reward for all horse owners
+    for horse in room.horses.values():
+        point_changes[horse.owner_id] = point_changes.get(horse.owner_id, 0) + config.PARTICIPANT_REWARD
+
     for bet in room.bets:
         point_changes[bet.user_id] = point_changes.get(bet.user_id, 0) - bet.amount
 
@@ -202,6 +206,10 @@ async def settle_race(room: Room) -> RaceResult | None:
     if not champion:
         return None
 
+    # Reward all participants
+    for horse in room.horses.values():
+        await points_service.reward_participant(horse.owner_id)
+
     # Reward champion owner
     await points_service.reward_champion(champion.owner_id)