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.

tests/js/snake-customizations.test.mjs

@@ -0,0 +1,21 @@
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import vm from 'node:vm';
+import test from 'node:test';
+
+const source = readFileSync(new URL('../../templates/files/js/Snake.js', import.meta.url), 'utf8');
+const SnakeUtils = vm.runInNewContext(`${source}\nSnakeUtils`);
+
+test('empty or missing head/tail uses the default SVG', () => {
+  for (const kind of ['heads', 'tails']) {
+    for (const value of [undefined, null, '', '   ']) {
+      assert.equal(SnakeUtils.buildCustomizationIconUrl(kind, value), `/dashboard/customizations/${kind}/default.svg`);
+    }
+  }
+});
+
+test('explicit customizations and invalid-name validation are preserved', () => {
+  assert.equal(SnakeUtils.buildCustomizationIconUrl('tails', 'ghost'), '/dashboard/customizations/tails/ghost.svg');
+  assert.equal(SnakeUtils.buildCustomizationIconUrl('heads', 'crystal-power'), '/dashboard/customizations/heads/crystal-power.svg');
+  assert.equal(SnakeUtils.buildCustomizationIconUrl('tails', '../ghost'), null);
+});