feat(ui): app sessions overlay the current page in every display mode

Launching an app (or opening a tx in mempool from Home/wallet/channels) used
to router.push the app-session page in overlay/fullscreen modes, swapping the
page underneath — confusing and lossy. All display modes are now store-driven:
panel renders beside the page, overlay/fullscreen render above it (teleported
to body), and the route never changes. Deep-link paths (/tx/<hash>) ride along
via the launcher's panelPath instead of a route query; closing always returns
exactly where the user was. The app-session route stays for direct links.

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

neode-ui/src/components/LightningChannelsPanel.vue

@@ -258,13 +258,11 @@
 
 <script setup lang="ts">
 import { ref, onMounted } from 'vue'
-import { useRouter } from 'vue-router'
 import { rpcClient } from '@/api/rpc-client'
+import { useAppLauncherStore } from '@/stores/appLauncher'
 
 defineProps<{ compact?: boolean }>()
 
-const router = useRouter()
-
 interface Channel {
   chan_id: string
   remote_pubkey: string
@@ -321,7 +319,8 @@ function fundingTxid(ch: Channel): string {
 
 function openInMempool(txid: string) {
   if (!txid) return
-  router.push({ name: 'app-session', params: { appId: 'mempool' }, query: { path: `/tx/${txid}` } })
+  // Overlay the explorer above the current page — never navigate away.
+  useAppLauncherStore().openSession('mempool', { path: `/tx/${txid}` })
 }
 
 function capacityPercent(amount: number, capacity: number): number {