feat: show rejoin link when bot is already in a fight

- Track active fight IDs per bot in orchestrator (Set → Map)
- Return fightId in "already in fight" error responses (409)
- Frontend shows "REJOIN FIGHT" link instead of generic error

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

frontend/src/pages/JoinBoutPage.vue

@@ -21,6 +21,7 @@ const step = ref<string>('login')
 const isHumanMode = ref(false)
 const selectedHumanSeed = ref('baby_fighter_1')
 const error = ref('')
+const activeFightLink = ref('')
 const rateLimitCountdown = ref(0)
 let rateLimitTimer: ReturnType<typeof setInterval> | null = null
 const isJoining = ref(false)
@@ -105,6 +106,7 @@ const archetypeList = [
 function handleError(e: unknown, fallback: string) {
   const msg = e instanceof Error ? e.message : fallback
   error.value = msg
+  activeFightLink.value = ''
   // Parse "Slow down" with retry seconds from the error message or check for countdown pattern
   if (msg.toLowerCase().includes('too many requests') || msg.toLowerCase().includes('slow down')) {
     startRateLimitTimer(msg)
@@ -394,8 +396,13 @@ async function fight() {
       return // Don't reset flag — navigation will unmount component
     } else {
       const data = await res.json()
-      const msg = data.retryAfterSec ? `${data.error} (${data.retryAfterSec}s)` : (data.error || 'Failed to join.')
-      handleError(new Error(msg), 'Failed to join.')
+      if (data.fightId) {
+        activeFightLink.value = data.fightId
+        error.value = 'You\'re already in a fight!'
+      } else {
+        const msg = data.retryAfterSec ? `${data.error} (${data.retryAfterSec}s)` : (data.error || 'Failed to join.')
+        handleError(new Error(msg), 'Failed to join.')
+      }
     }
   } catch {
     error.value = 'Network error.'
@@ -443,8 +450,13 @@ async function practice() {
       return // Don't reset flag — navigation will unmount component
     } else {
       const data = await res.json()
-      const msg = data.retryAfterSec ? `${data.error} (${data.retryAfterSec}s)` : (data.error || 'Failed to start practice fight.')
-      handleError(new Error(msg), 'Practice fight failed.')
+      if (data.fightId) {
+        activeFightLink.value = data.fightId
+        error.value = 'You\'re already in a fight!'
+      } else {
+        const msg = data.retryAfterSec ? `${data.error} (${data.retryAfterSec}s)` : (data.error || 'Failed to start practice fight.')
+        handleError(new Error(msg), 'Practice fight failed.')
+      }
     }
   } catch {
     error.value = 'Network error.'
@@ -1144,6 +1156,14 @@ function handleSignOut() {
       <!-- Error display -->
       <div v-if="error" class="mt-4 p-3 border-2 border-ko/30 bg-ko/5 text-center">
         <p class="font-mono text-xs text-ko">{{ error }}</p>
+        <RouterLink
+          v-if="activeFightLink"
+          :to="`/arena/${activeFightLink}`"
+          class="inline-block mt-2 px-6 py-2 bg-neon-cyan/10 border-2 border-neon-cyan text-neon-cyan
+                 font-display font-black text-xs tracking-widest hover:bg-neon-cyan/20 transition-all neon-border-cyan"
+        >
+          REJOIN FIGHT
+        </RouterLink>
         <div v-if="rateLimitCountdown > 0" class="mt-2 flex items-center justify-center gap-2">
           <div class="w-4 h-4 border-2 border-neon-purple/60 border-t-neon-purple rounded-full animate-spin" />
           <p class="font-display font-bold text-sm text-neon-purple tracking-wider">