Add bandit priors for shadow meta-controller

syncpatch/train-policy-offline

@@ -52,6 +52,8 @@ def main() -> int:
                 'success': success,
                 'failure_like': failure,
                 'avg_reward': (reward_sum / count if count else 0.0),
+                'alpha': success + 1.0,
+                'beta': failure + 1.0,
                 'beta_mean': beta_mean(success, failure),
                 'mode': classify_mode(row),
             }