feat: add gameplay stats and restore Zenith rollout depth

- Add read-only gameplay statistics with filters and opponent comparisons.
- Report move-trace latency percentiles and external timeout counts.
- Pair engine latency with the preceding turn to separate timing stages.
- Adjust Zenith rollout deepening for its larger timeout reserve.
- Bump Zenith to 1.2.0 and document the fix and snake-stats command.
- Cover statistics, trace aggregation, rollout depth, and verdict budgets.

justfile

@@ -90,6 +90,15 @@ db *args:
   command -v psql >/dev/null || { echo "Install the PostgreSQL client (psql) first." >&2; exit 1; }
   exec psql --dbname="$GAMEPLAY_DB_PG_DSN" "$@"
 
+# Read-only win stats per own snake version and per opponent (extra args are passed through)
+[positional-arguments]
+snake-stats *args:
+  #!/usr/bin/env bash
+  set -euo pipefail
+
+  : "${GAMEPLAY_DB_PG_DSN:?Set GAMEPLAY_DB_PG_DSN in .env or the environment}"
+  PYTHONPATH="{{justfile_directory()}}" uv run python "{{justfile_directory()}}/scripts/gameplay_snake_stats.py" "$@"
+
 cleanup-gameplay-postgres older_than_days="30" execute="false" vacuum="false":
   #!/usr/bin/env bash
   set -euo pipefail