fix(wallet): channel funding-tx link uses the explorer flow + consent modal above nested modals

The Channels panel's 'Funding tx in Mempool' link still hardcoded the
local app (missed in the explorer rollout): now it routes like every
other tx link — local Mempool when running, else the saved external
explorer, with the first-time consent modal setting it up and then
opening the tx. The consent modal moves to z-3600 so it renders above
the Wallet Settings modal that can trigger it.

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

neode-ui/src/components/ExternalExplorerModal.vue

@@ -1,8 +1,12 @@
 <template>
+  <!-- z-3600: this consent prompt can be triggered from INSIDE another
+       modal (e.g. Wallet Settings → Channels → funding tx), so it must sit
+       above the standard modal layer (3000) but below the app overlay (4000). -->
   <BaseModal
     :show="!!explorer.pendingTx.value"
     title="Open on an external explorer?"
     max-width="max-w-md"
+    z-index="z-[3600]"
     @close="explorer.cancelPending()"
   >
     <!-- Same visual language as the uninstall keep-your-data warning: amber