fix(media): loader before peer video/audio plays + accurate error (B3/B22)

Streaming a peer file connects over mesh/Tor before the first frame, so the
player sat blank. Add a loading state:
- PeerFiles video modal: spinner overlay ("Connecting to peer…") until the
  <video> fires playing/canplay; an error overlay on failure instead of a
  silent black box.
- useAudioPlayer: loading flag driven by loadstart/waiting vs canplay/playing;
  GlobalAudioPlayer shows a spinner in the transport button while connecting.
- Fix the misleading audio error "Could not play audio. File Browser may not be
  running." (wrong for peer content) → "Could not play this audio file. The peer
  may be offline…" (B22).

type-check clean; useAudioPlayer tests 10/10.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/components/GlobalAudioPlayer.vue

@@ -25,7 +25,11 @@
             class="flex-shrink-0 w-9 h-9 rounded-full bg-white/10 hover:bg-white/20 flex items-center justify-center transition-colors"
             @click="togglePlay"
           >
-            <svg v-if="!audioPlayer.playing.value" class="w-5 h-5 text-white ml-0.5" fill="currentColor" viewBox="0 0 24 24">
+            <svg v-if="audioPlayer.loading.value" class="w-5 h-5 animate-spin text-white" fill="none" viewBox="0 0 24 24">
+              <circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4" />
+              <path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.4 0 0 5.4 0 12h4z" />
+            </svg>
+            <svg v-else-if="!audioPlayer.playing.value" class="w-5 h-5 text-white ml-0.5" fill="currentColor" viewBox="0 0 24 24">
               <path d="M8 5v14l11-7L8 5z" />
             </svg>
             <svg v-else class="w-5 h-5 text-white" fill="currentColor" viewBox="0 0 24 24">