feat: streaming ecash payments + media playback overhaul

Cashu ecash protocol (BDHKE blind signatures, cashuA token format,
mint HTTP client) replacing the stub wallet. TollGate-inspired streaming
data payment system with step-based pricing (bytes/time/requests),
session management with incremental top-ups, usage metering, and
Nostr kind 10021 service advertisements.

13 new streaming.* RPC endpoints. Content server now verifies real
Cashu tokens. Profits tracking includes streaming revenue.

Frontend: GlobalAudioPlayer (persistent bottom bar across all pages),
video lightbox with full controls, audio in MediaLightbox, free file
previews (no blur), paid 10% audio/video previews, separated play
vs download buttons in PeerFiles.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/App.vue

@@ -37,6 +37,9 @@
     <!-- PWA Install Prompt (Install app, not just Add to Home Screen) -->
     <PWAInstallPrompt />
 
+    <!-- Global persistent audio player (bottom bar) -->
+    <GlobalAudioPlayer />
+
     <!-- Toast notifications - top right, glass style, any page -->
     <Teleport to="body">
       <Transition name="toast">
@@ -75,6 +78,7 @@ import AppLauncherOverlay from './components/AppLauncherOverlay.vue'
 import ToastStack from './components/ToastStack.vue'
 import Screensaver from './components/Screensaver.vue'
 import HelpGuideModal from './components/HelpGuideModal.vue'
+import GlobalAudioPlayer from './components/GlobalAudioPlayer.vue'
 
 import { useControllerNav } from '@/composables/useControllerNav'
 import { playKeyboardTypingSound } from '@/composables/useLoginSounds'