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/pages/FightPage.vue

@@ -11,7 +11,7 @@ import {
   fanfareRound,
   sfxCrowdCheer, sfxApplause, sfxDrumRoll,
   announceFinishHim, announceFlawlessVictory, announceDeepIntro,
-  setMusicIntensity, stopAllAudio, ensureAudioContext, setMasterMute,
+  setMusicIntensity, stopAllAudio, ensureAudioContext, installAutoUnlock, setMasterMute,
 } from '../game/audio'
 
 const route = useRoute()
@@ -444,6 +444,9 @@ watch(liveFightData, async (val) => {
 
 // --- Mount / Unmount ---
 onMounted(async () => {
+  // Auto-unlock AudioContext on first user interaction (critical for mobile TTS)
+  if (liveSoundOn.value) installAutoUnlock()
+
   let status = await loadFight()
 
   // If fetch failed (offline), try IndexedDB cache