fix: SSE reconnection with exponential backoff (BUG-F1)

SSE now always attempts reconnection when fight isn't finished,
regardless of isLive.value. Uses exponential backoff (1s, 2s, 4s,
max 8s). Moved sseRetries to outer scope to persist across reconnects.

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

frontend/src/composables/useFightPolling.ts

@@ -36,6 +36,7 @@ export function useFightPolling(fightId: Ref<string>) {
   let pollHandle: ReturnType<typeof setInterval> | null = null
   let pollCount = 0
   let eventSource: EventSource | null = null
+  let sseRetries = 0
   const sseListeners: SSEListenerEntry[] = []
 
   // --- Load fight data ---
@@ -182,17 +183,18 @@ export function useFightPolling(fightId: Ref<string>) {
       }
     })
 
-    let sseRetries = 0
     eventSource.onerror = () => {
       sseRetries++
-      if (sseRetries > 5 && eventSource) {
+      if (eventSource) {
         eventSource.close()
         eventSource = null
-        const delay = Math.min(1000 * 2 ** (sseRetries - 5), 10000)
-        setTimeout(() => {
-          if (isLive.value && !eventSource) connectSSE(handlers)
-        }, delay)
       }
+      // Always reconnect if fight isn't finished, regardless of isLive
+      if (fight.value?.status === 'finished') return
+      const delay = Math.min(1000 * 2 ** (sseRetries - 1), 8000) // 1s, 2s, 4s, 8s max
+      setTimeout(() => {
+        if (!eventSource && fight.value?.status !== 'finished') connectSSE(handlers)
+      }, delay)
     }
     eventSource.onopen = () => { sseRetries = 0 }
   }