fix: human vs AI fight bugs — CSP for TTS, invisible sprites, fight end sequence

- Allow huggingface.co in CSP connect-src (fixes Kokoro TTS model download)
- Add registerSW.js route (fixes PWA service worker 404)
- Add _resetPositions() safety after entrance (fixes invisible fighters)
- Fight end sequence works without canvas scene (KO/overlays/log always play)
- Pre-fight instructions in battle log for human players
- NIP-55 visibility sync and cleanup handlers

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

frontend/src/pages/FightPage.vue

@@ -170,6 +170,13 @@ async function initLiveScene() {
     { type: 'system', round: 0, text: `${data.botA.name} vs ${data.botB.name}`, color: 'text-secondary' },
     { type: 'divider', round: 0, text: '', color: '' },
   )
+  // Pre-fight instructions for human players
+  if (isHumanFight.value) {
+    liveLogItems.value.push(
+      { type: 'narration', round: 0, text: 'HUMAN VS AI — Answer challenges faster and better than the bot! Tap a choice or type your answer before time runs out.', color: 'neon-yellow' },
+      { type: 'divider', round: 0, text: '', color: '' },
+    )
+  }
   scrollLiveLog()
 }
 
@@ -320,7 +327,7 @@ async function handleFightEnd(data: any) {
     else liveHpA.value = 0
   }
 
-  if (liveScene && data.winnerId) {
+  if (data.winnerId) {
     const winningSide = (data.winnerId === fd.botA.id ? 'a' : 'b') as 'a' | 'b'
 
     sfxDrumRoll()
@@ -328,11 +335,21 @@ async function handleFightEnd(data: any) {
     announceFinishHim()
     await showLiveOverlay('FINISH IT!', '#ff2d2d', 900)
 
-    if (data.isPerfect) {
-      await liveScene.playPerfect(winningSide, data.winnerName)
-      announceFlawlessVictory()
+    if (liveScene) {
+      try {
+        if (data.isPerfect) {
+          await liveScene.playPerfect(winningSide, data.winnerName)
+          announceFlawlessVictory()
+        } else {
+          await liveScene.playKO(winningSide, data.winnerName)
+        }
+      } catch (err) {
+        console.warn('[FightPage] KO animation failed:', err)
+      }
     } else {
-      await liveScene.playKO(winningSide, data.winnerName)
+      // Scene unavailable — still announce vocally
+      if (data.isPerfect) announceFlawlessVictory()
+      await sleep(800)
     }
 
     sfxApplause()
@@ -341,7 +358,7 @@ async function handleFightEnd(data: any) {
     if (data.mode === 'ranked' && data.potSats) {
       await showLiveOverlay(`WON ${data.potSats} SATS!`, '#00f0ff', 1500)
     }
-    liveScene.stopMusic()
+    if (liveScene) liveScene.stopMusic()
   }
 
   if (isHumanFight.value) {