fix: track and clear all intervals and event listeners

- FightPage.vue: store SSE listener refs in array, removeEventListener
  on each before close() in disconnectSSE()
- FightScene.ts: add cleanupTimers Set with trackedInterval/trackedTimeout
  helpers; replace key setInterval calls (projectile trails, entrance
  flames, talking animation, exhaust effects, dimensional shift, hole
  fade) with tracked versions; clear all on scene destroy()
- rate-limit.ts: export cleanupInterval handle for graceful shutdown

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

frontend/src/pages/FightPage.vue

@@ -389,17 +389,24 @@ async function initLiveScene() {
 }
 
 // --- SSE connection ---
+const sseListeners: { event: string; handler: EventListener }[] = []
+
+function addSSEListener(es: EventSource, event: string, handler: (e: MessageEvent) => void) {
+  es.addEventListener(event, handler as EventListener)
+  sseListeners.push({ event, handler: handler as EventListener })
+}
+
 function connectSSE() {
   eventSource = new EventSource(`/api/fights/${fightId.value}/stream`)
 
-  eventSource.addEventListener('spectator_count', (e) => {
+  addSSEListener(eventSource, 'spectator_count', (e) => {
     try {
       const data = JSON.parse(e.data)
       spectatorCount.value = data.count || 0
     } catch { /* ignore */ }
   })
 
-  eventSource.addEventListener('ping', (e) => {
+  addSSEListener(eventSource, 'ping', (e) => {
     try {
       if (e.data) {
         const data = JSON.parse(e.data)
@@ -408,21 +415,19 @@ function connectSSE() {
     } catch { /* ignore */ }
   })
 
-  eventSource.addEventListener('reaction', (e) => {
+  addSSEListener(eventSource, 'reaction', (e) => {
     try {
       const data = JSON.parse(e.data)
       if (data.emoji && data.counts) {
-        // Spawn floating emoji in the live view
         spawnLiveReactionEmoji(data.emoji)
       }
     } catch { /* ignore */ }
   })
 
-  eventSource.addEventListener('round_start', (e) => {
+  addSSEListener(eventSource, 'round_start', (e) => {
     try {
       const data = JSON.parse(e.data)
       currentChallengeInfo.value = { type: data.challenge.type, label: data.challenge.label }
-      // Show challenge question in battle log
       liveLogItems.value.push({
         type: 'challenge',
         round: data.round,
@@ -435,10 +440,9 @@ function connectSSE() {
     }
   })
 
-  eventSource.addEventListener('human_challenge', async (e) => {
+  addSSEListener(eventSource, 'human_challenge', async (e) => {
     try {
       const sseData = JSON.parse(e.data)
-      // Fetch from API to get choices (SSE event doesn't include them)
       if (myBot.value) {
         const res = await fetch(`/api/fights/${fightId.value}/challenge/${myBot.value.id}`)
         if (res.ok) {
@@ -453,7 +457,6 @@ function connectSSE() {
           }
         }
       }
-      // Fallback: use SSE data without choices
       if (roundCooldown.value > 0) {
         pendingChallengeData.value = { data: sseData, receivedAt: Date.now() }
       } else {
@@ -464,7 +467,7 @@ function connectSSE() {
     }
   })
 
-  eventSource.addEventListener('round_end', (e) => {
+  addSSEListener(eventSource, 'round_end', (e) => {
     try {
       const data = JSON.parse(e.data)
       if (data.spectators !== undefined) spectatorCount.value = data.spectators
@@ -474,7 +477,7 @@ function connectSSE() {
     }
   })
 
-  eventSource.addEventListener('fight_end', (e) => {
+  addSSEListener(eventSource, 'fight_end', (e) => {
     try {
       const data = JSON.parse(e.data)
       if (data.spectators !== undefined) spectatorCount.value = data.spectators
@@ -486,7 +489,6 @@ function connectSSE() {
 
   let sseRetries = 0
   eventSource.onerror = () => {
-    // EventSource auto-reconnects, but if it keeps failing, reconnect manually with backoff
     sseRetries++
     if (sseRetries > 5 && eventSource) {
       eventSource.close()
@@ -501,7 +503,14 @@ function connectSSE() {
 }
 
 function disconnectSSE() {
-  if (eventSource) { eventSource.close(); eventSource = null }
+  if (eventSource) {
+    for (const { event, handler } of sseListeners) {
+      eventSource.removeEventListener(event, handler)
+    }
+    sseListeners.length = 0
+    eventSource.close()
+    eventSource = null
+  }
   spectatorCount.value = 0
 }