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.

snakes/__init__.py

@@ -13,7 +13,7 @@ SNAKE_REGISTRATIONS = {
     "snakes.strategies.prism", "1.5.0"
   ),
   "ZenithBattleSnake_ClaudeOpus5_5": SnakeRegistration(
-    "snakes.strategies.zenith", "1.1.0"
+    "snakes.strategies.zenith", "1.2.0"
   ),
   "DummSnake": SnakeRegistration("snakes.legacy.DummSnake", "1.0.0"),
   "LogicSnake": SnakeRegistration("snakes.legacy.LogicSnake", "1.1.0"),