fix: mobile nostr signer detection, mobile TTS auto-unlock, button loaders

- Nostr signer: poll for window.nostr up to 3s on mobile (Amber injects
  late). Both login() and handleSignerLogin() now wait before failing.
- Mobile TTS: install global one-time click/touch/keydown handler to
  auto-unlock AudioContext when fight pages mount. Previously only
  triggered by explicit sound toggle, so mobile TTS silently failed.
- Add loading spinners to "I BUILD BOTS" and "I FIGHT MYSELF" buttons.

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

frontend/src/components/FightViewer.vue

@@ -7,7 +7,7 @@ import {
   announceFinishHim, announceFlawlessVictory,
   sfxCrowdCheer, sfxCrowdGasp, sfxCrowdOoh, sfxApplause, sfxDrumRoll,
   setMusicIntensity, stopAllAudio,
-  setMasterMute, isMasterMuted, ensureAudioContext,
+  setMasterMute, isMasterMuted, ensureAudioContext, installAutoUnlock,
   speakQuestion, speakAnswer, speakNarration,
   prefetchQuestion, prefetchAnswer, prefetchNarration,
   awaitQuestionReady, awaitAnswerReady,
@@ -144,6 +144,9 @@ function togglePerfMode() {
 const logItems = ref<{ type: string; round: number; text: string; color: string }[]>([])
 
 onMounted(async () => {
+  // Auto-unlock AudioContext on first user interaction (critical for mobile TTS)
+  if (soundOn.value) installAutoUnlock()
+
   if (props.autoplay) {
     // Fresh fight — replay() will call initScene(), no need to double-init
     await nextTick()