feat: add Zenith strategy and move latency tracing

- Register Zenith 1.1 with balanced duel verdicts and forced-outcome overrides.
- Prioritize permanent-trail space in Constrictor and health-aware hazard routes.
- Deduct executor queue delays and return fallback directions on move timeouts.
- Correlate response headers, replay timings, and sampled structured trace logs.
- Move shared metrics publication off the response path without losing local counts.
- Allow configurable tournament opponents and add a psql helper recipe.
- Preserve empty latency values through compact replay encoding and migration.
- Update Arena game links and use default assets for missing customizations.
- Cover strategy, HTTP lifecycle, tracing, replay codecs, and dashboard behavior.
- Validate with 260 passing Python tests, 4 skips, and 2 passing JavaScript tests.

server/services/move_trace.py

@@ -0,0 +1,49 @@
+"""Small request-local timings; no board payloads or external tracing dependency."""
+from contextlib import contextmanager
+import json
+import os
+from threading import Lock
+from time import perf_counter
+from uuid import uuid4
+
+class MoveTrace:
+  def __init__(self, game_id, turn):
+    self.id = uuid4().hex
+    self.game_id = game_id
+    self.turn = turn
+    self.started = perf_counter()
+    self._lock = Lock()
+    self._fields = {}
+
+  def set(self, **fields):
+    with self._lock:
+      self._fields.update(fields)
+
+  @contextmanager
+  def stage(self, name):
+    started = perf_counter()
+    try:
+      yield
+    finally:
+      self.set(**{name + '_ms': round((perf_counter() - started) * 1000, 3)})
+
+  def snapshot(self):
+    with self._lock:
+      return {'trace_id': self.id, **self._fields}
+
+  def log(self, logger):
+    fields = self.snapshot()
+    # Every timeout/slow request, plus deterministic sampling of normal moves.
+    try:
+      sample = max(0, int(os.getenv('MOVE_TRACE_SAMPLE_EVERY', '100')))
+      slow_ms = max(0, float(os.getenv('MOVE_TRACE_SLOW_MS', '300')))
+    except ValueError:
+      sample, slow_ms = 100, 300
+    slow_stage = any(value >= slow_ms for key, value in fields.items()
+                     if key.endswith('_ms') and isinstance(value, (int, float)))
+    if not (fields.get('timed_out') or fields.get('metrics_publish_failed') or slow_stage
+            or (sample and int(self.id[:8], 16) % sample == 0)):
+      return
+    logger.info('move_trace %s', json.dumps({
+      'game_id': self.game_id, 'turn': self.turn, **fields,
+    }, separators=(',', ':')))