fix(demo-ui): demoable apps launch in-frame; 'Not available in demo' label

- Register the 8 new placeholder apps in DEMO_MOCK_UI so they're launchable
  and installable in the demo.
- Demo bypasses the new-tab/tab-launch lists for demoable apps — they're
  served same-origin by the mock backend with no framing headers, so they
  render in the in-app session instead of opening broken localhost tabs.
- Non-demoable apps now say 'Not available in demo' instead of 'No demo'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/views/discover/AppGrid.vue

@@ -121,7 +121,7 @@
             v-else-if="IS_DEMO && !isInstalled(app.id) && !isDemoApp(app.id)"
             disabled
             class="flex-1 px-4 py-2 bg-white/10 rounded-lg text-white/40 text-sm font-medium cursor-not-allowed"
-          >No demo</button>
+          >Not available in demo</button>
           <!-- Install button -->
           <button
             v-else-if="!isInstalled(app.id) && (app.source === 'local' || app.dockerImage)"

neode-ui/src/views/discover/FeaturedApps.vue

@@ -78,7 +78,7 @@
             v-else-if="IS_DEMO && !isInstalled(app.id) && !isDemoApp(app.id)"
             disabled
             class="glass-button glass-button-sm rounded-lg text-sm font-medium opacity-50 cursor-not-allowed"
-          >No demo</button>
+          >Not available in demo</button>
           <button
             v-else-if="!isInstalled(app.id) && app.dockerImage"
             data-controller-install-btn