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/JoinBoutPage.vue

@@ -33,6 +33,7 @@ const queueCount = ref(0)
 const rankedQueueCount = ref(0)
 const rankedEstWait = ref(15)
 let pollHandle: ReturnType<typeof setInterval> | null = null
+let nip55ReturnHandler: (() => void) | null = null
 
 // Registration form
 const selectedArchetype = ref('standard')
@@ -161,11 +162,13 @@ onMounted(async () => {
 onBeforeRouteLeave(() => {
   if (pollHandle) { clearInterval(pollHandle); pollHandle = null }
   if (rateLimitTimer) { clearInterval(rateLimitTimer); rateLimitTimer = null }
+  if (nip55ReturnHandler) { document.removeEventListener('visibilitychange', nip55ReturnHandler); nip55ReturnHandler = null }
 })
 
 onUnmounted(() => {
   if (pollHandle) clearInterval(pollHandle)
   if (rateLimitTimer) { clearInterval(rateLimitTimer); rateLimitTimer = null }
+  if (nip55ReturnHandler) { document.removeEventListener('visibilitychange', nip55ReturnHandler); nip55ReturnHandler = null }
 })
 
 async function pollQueue() {
@@ -212,6 +215,45 @@ async function handleSignerLogin() {
       // On Android, try NIP-55 intent to open Amber/Primal directly
       if (hasAndroidSigner.value) {
         error.value = 'Opening signer app...'
+
+        // Listen for return from signer app (user switches back to browser)
+        if (nip55ReturnHandler) document.removeEventListener('visibilitychange', nip55ReturnHandler)
+        nip55ReturnHandler = async () => {
+          if (document.visibilityState !== 'visible') return
+          document.removeEventListener('visibilitychange', nip55ReturnHandler!)
+          nip55ReturnHandler = null
+
+          // Check if signer redirected with callback params in the URL
+          try {
+            const nip55Result = await processNip55Return()
+            if (nip55Result) {
+              error.value = ''
+              if (nip55Result.bot) {
+                isHumanMode.value = !!nip55Result.bot.isHuman
+                step.value = 'ready'
+              } else {
+                step.value = 'choose-mode'
+              }
+              return
+            }
+          } catch {
+            // Callback params present but auth failed
+            error.value = 'Signer login failed. Try again.'
+            return
+          }
+
+          // No callback params — signer may have injected window.nostr
+          error.value = 'Connecting...'
+          const signerFound = await waitForSigner(2000)
+          if (signerFound) {
+            error.value = ''
+            handleLogin()
+          } else {
+            error.value = 'Signer did not return a signed event. Tap to try again.'
+          }
+        }
+        document.addEventListener('visibilitychange', nip55ReturnHandler)
+
         initiateNip55Login()
         return
       }