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/engine/fight-loop.ts

@@ -132,6 +132,12 @@ export async function startFightLoop(options: FightLoopOptions = {}): Promise<vo
         )
       }
 
+      // Log memory usage every 10 fights
+      if (fightCount % 10 === 0) {
+        const mem = process.memoryUsage()
+        console.log(`[fight-loop] memory #${fightCount}: rss=${Math.round(mem.rss / 1024 / 1024)}MB heap=${Math.round(mem.heapUsed / 1024 / 1024)}/${Math.round(mem.heapTotal / 1024 / 1024)}MB`)
+      }
+
       // Wait before next fight
       if (fightCount < maxFights) {
         await sleep(intervalMs + Math.floor(Math.random() * intervalMs * 0.5))