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/composables/useCompanionIntro.ts

@@ -0,0 +1,13 @@
+import { ref } from 'vue'
+
+/**
+ * Cross-view trigger for the Remote Companion intro/pairing modal
+ * (CompanionIntroOverlay, mounted once in Dashboard.vue). Views like the
+ * App Store banner call openCompanionIntro() to pop it on demand — this
+ * bypasses the once-per-browser auto-show gate.
+ */
+export const companionIntroRequested = ref(false)
+
+export function openCompanionIntro(): void {
+  companionIntroRequested.value = true
+}