Add --wandb-notes flag for run purpose description

Exposes wandb.init's notes field through the CLI so each run can carry a
short description of its purpose, visible on the W&B run page alongside
tags and config.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/coolrl_lost_cities/games/classic/deep_cfr/cli.py

@@ -106,6 +106,7 @@ def train_command(args: argparse.Namespace) -> None:
                 config=config.to_dict(),
                 run_dir=str(run_dir),
                 tags=list(args.wandb_tag) if args.wandb_tag else None,
+                notes=args.wandb_notes,
             )
         )
     trainer = DeepCFRTrainer(
@@ -251,6 +252,10 @@ def main(argv: list[str] | None = None) -> None:
         default=[],
         help="Tag to attach to the W&B run (repeatable).",
     )
+    train.add_argument(
+        "--wandb-notes",
+        help="Free-form note describing this run's purpose (shown on the W&B run page).",
+    )
     train.set_defaults(func=train_command)
 
     evaluate = subparsers.add_parser("eval")

src/coolrl_lost_cities/games/classic/deep_cfr/tracking.py

@@ -71,6 +71,7 @@ class WandbRunTracker:
         mode: str | None = None,
         config: dict[str, Any] | None = None,
         tags: list[str] | None = None,
+        notes: str | None = None,
     ):
         try:
             import wandb
@@ -88,6 +89,7 @@ class WandbRunTracker:
             config=config or {},
             dir=str(run_dir_path),
             tags=tags,
+            notes=notes,
             reinit=True,
         )