feat(ui): companion app banner in the App Store + APK download unblocked

The App Store gains a "Your Node. In Your Pocket." hero banner for the
mobile companion app, in the same format as the featured-app banner, with
the app running on a phone mockup rising out of the right edge. Install
(or clicking anywhere on it) opens the Remote Companion download/pairing
modal — now openable on demand via a shared trigger instead of only
auto-showing once.

Also fixes the companion APK download on PWA installs: /packages/ now
bypasses the service worker's SPA fallback, which was answering the
download click with index.html instead of the file.

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

neode-ui/src/components/CompanionIntroOverlay.vue

@@ -59,6 +59,7 @@
                   class="flex-1 inline-flex items-center justify-center rounded-lg bg-orange-500/20 border border-orange-500/30 px-3 py-2.5 text-sm font-medium text-orange-400 hover:bg-orange-500/30 transition-colors text-center"
                   target="_blank"
                   rel="noopener noreferrer"
+                  download
                 >
                   Download app
                 </a>
@@ -132,6 +133,7 @@
 import { ref, onMounted, onUnmounted, watch } from 'vue'
 import * as QRCode from 'qrcode'
 import { IS_DEMO, DEMO_PASSWORD } from '@/composables/useDemoIntro'
+import { companionIntroRequested } from '@/composables/useCompanionIntro'
 import { useLoginTransitionStore } from '@/stores/loginTransition'
 import { rpcClient } from '@/api/rpc-client'
 
@@ -202,6 +204,18 @@ function maybeShow() {
   }, 250)
 }
 
+// Manual open (App Store banner etc.) — ignores the once-per-browser gate.
+watch(companionIntroRequested, (requested) => {
+  if (!requested) return
+  companionIntroRequested.value = false
+  if (calmTicker) {
+    clearInterval(calmTicker)
+    calmTicker = null
+  }
+  step.value = 'download'
+  visible.value = true
+})
+
 watch(visible, async (isVisible) => {
   if (!isVisible) return
   qrDataUrl.value = await QRCode.toDataURL(companionDownloadUrl, {