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.

snakes/engine/health_routes.py

@@ -0,0 +1,29 @@
+"""Health-cost routes to food or non-hazard refuge, with current bodies fixed."""
+import heapq
+
+def health_route_cost(start, food, hazards, stacks, damage, blocked, width, height, *, refuge=False):
+  """Cost until food resets health, or until leaving hazards for refuge.
+
+  Food is consumed before elimination, so its final step needs no remaining
+  health. Other steps must leave health positive. Bodies remain obstacles,
+  including food-covered body cells; the caller removes the starting head.
+  """
+  queue = [(0, start)]
+  best = {start: 0}
+  while queue:
+    cost, point = heapq.heappop(queue)
+    if cost != best[point]:
+      continue
+    if point in food or (refuge and point not in hazards):
+      return cost
+    x, y = point
+    for target in ((x, y + 1), (x, y - 1), (x - 1, y), (x + 1, y)):
+      nx, ny = target
+      if not (0 <= nx < width and 0 <= ny < height) or target in blocked:
+        continue
+      step = 0 if target in food else 1 + (damage * stacks.get(target, 1) if target in hazards else 0)
+      value = cost + step
+      if value < best.get(target, float('inf')):
+        best[target] = value
+        heapq.heappush(queue, (value, target))
+  return None

snakes/engine/survival_search.py

@@ -235,7 +235,7 @@ class CompactSurvivalSearch:
     blocked = self._occupied(mine, enemies) & ~(1 << mine[0])
     space = self.board.flood_count(mine[0], blocked)
     liberties = self.board.open_neighbor_count(mine[0], blocked)
-    if liberties == 0 or space < len(mine):
+    if liberties == 0 or (not self.is_constrictor and space < len(mine)):
       return self.DEATH
     enemy_pressure = 0.0
     for enemy in enemies: