test: add fight loop throughput benchmark (>500 fights/sec)

Benchmarks the scoring pipeline (challenge → response → score → elo → tier)
without I/O. Currently achieves ~8500 fights/sec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/engine/lifecycle.test.ts

@@ -504,4 +504,45 @@ describe('fight lifecycle', () => {
         .toBeLessThanOrEqual(expectedAWinMax)
     }
   })
+
+  it('fight loop throughput: >500 fights/second (no I/O)', () => {
+    const fights = 5000
+    const start = performance.now()
+
+    for (let f = 0; f < fights; f++) {
+      const eloA = 1000 + (f % 10) * 100
+      const eloB = 1000 + ((f * 3) % 10) * 100
+      const botA = { id: 'perf-a', name: 'PerfA' }
+      const botB = { id: 'perf-b', name: 'PerfB' }
+      const usedTypes = new Set<string>()
+      let comboA = 0
+      let comboB = 0
+      const rounds = 7 + (f % 4)
+
+      for (let r = 0; r < rounds; r++) {
+        const challenge = pickChallenge(usedTypes, null, undefined, r + 1)
+        usedTypes.add(challenge.type)
+        const respA = mockResponse(challenge, 'confident', eloA)
+        const respB = mockResponse(challenge, 'clueless', eloB)
+        const result = scoreRound(
+          challenge, botA, botB,
+          { answer: respA.answer, timeMs: respA.timeMs, timedOut: respA.timedOut, error: respA.error },
+          { answer: respB.answer, timeMs: respB.timeMs, timedOut: respB.timedOut, error: respB.error },
+          null, comboA, comboB,
+        )
+        if (result.winnerId === botA.id) { comboA++; comboB = 0 }
+        else if (result.winnerId === botB.id) { comboB++; comboA = 0 }
+      }
+
+      // Elo + tier calculation
+      calculateElo(eloA, eloB)
+      calculateTier(eloA, f % 50, f % 20)
+    }
+
+    const elapsed = performance.now() - start
+    const fightsPerSec = Math.round(fights / (elapsed / 1000))
+
+    // Must process >500 fights/sec (scoring pipeline only, no I/O)
+    expect(fightsPerSec).toBeGreaterThan(500)
+  })
 })