perf: server memory leak audit

Add periodic cleanup of fightReactions Map (clears when >100 entries).
Add RSS/heap logging every 10 fights in fight-loop for memory monitoring.
Set --max-old-space-size=256 in Docker CMD as safety net.

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

server/src/routes/fights.ts

@@ -25,6 +25,13 @@ let activeSSECount = 0
 const ssePerIp = new Map<string, number>()
 const MAX_SSE_PER_IP = 5
 
+// Periodic cleanup of stale reaction data (every 10 minutes)
+setInterval(() => {
+  if (fightReactions.size > 100) {
+    fightReactions.clear()
+  }
+}, 10 * 60_000)
+
 export function getActiveSSECount(): number {
   return activeSSECount
 }