feat: add Discover page — cypherpunk app store with sovereignty messaging

- New Discover.vue with hero banner, featured sovereignty stack apps,
  principle cards, manifesto footer, and full app grid
- Featured apps (Bitcoin Knots, LND, BTCPay, Vaultwarden) with
  expanded privacy/sovereignty descriptions
- Discover is first tab in categories bar on App Store pages
- Smart back navigation: detail pages return to Discover when navigated from there
- Category clicks from Discover navigate to Marketplace with category pre-selected
- Cypherpunk aesthetic: terminal tags, scanline overlays, gradient accents,
  animated Bitcoin orange headings
- Global CSS classes: discover-hero, discover-terminal-tag, discover-featured-card,
  discover-principle-card, discover-manifesto
- Route added: /dashboard/discover

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

neode-ui/src/views/MarketplaceAppDetails.vue

@@ -506,7 +506,11 @@ function handleImageError(e: Event) {
 }
 
 function goBack() {
-  router.push('/dashboard/marketplace').catch(() => {})
+  if (route.query.from === 'discover') {
+    router.push('/dashboard/discover').catch(() => {})
+  } else {
+    router.push('/dashboard/marketplace').catch(() => {})
+  }
 }
 
 function goToInstalledApp() {