Fix single-player tournament: set commit_label default (was KeyError in _round_message)

The commit-label refactor added Player._round_message reading config['commit_label'],
which PvP/ladder set but single-player did not, breaking test_single_player_battlesnake.

Author: john-b-yang

codeclash/tournaments/single_player.py

@@ -62,6 +62,9 @@ def get_game_context(self, agent_config: dict, *, round: int) -> GameContext:
 
     def get_agent(self, agent_config: dict, round: int) -> Player:
         """Create an agent with environment and game context."""
+        # Commit/tag messages are prefixed with `commit_label` (see Player._round_message);
+        # single-player has no rung/opponent prefix, so default it to empty (as PvP does).
+        agent_config.setdefault("commit_label", "")
         environment = self.game.get_environment(f"{self.game.game_id}.{agent_config['name']}")
         game_context = self.get_game_context(agent_config, round=round)
         return get_agent(agent_config, game_context, environment)