feat(wallet): external tx-explorer fallback with consent + On-chain settings tab

Pruned nodes can't run the Mempool app, but tx links blindly opened it
anyway. Now: local app when running; otherwise an external explorer
(default tx1138.com) behind a one-time amber consent modal that spells
out what the other server's operator learns (tx of interest + IP) and
lets the user point at their own instance (placeholder mempool.guide).
Wallet Settings gains an On-chain tab (explorer URL + don't-warn toggle);
tabs renamed Cashu/Fedi so five fit in the row.

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

neode-ui/src/views/web5/Web5Wallet.vue

@@ -151,7 +151,7 @@ import { ref } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { formatTxTime } from './utils'
 import type { WalletTransaction } from './types'
-import { useAppLauncherStore } from '@/stores/appLauncher'
+import { useTxExplorer } from '@/composables/useTxExplorer'
 
 const { t } = useI18n()
 
@@ -177,8 +177,10 @@ defineEmits<{
   openReceive: []
 }>()
 
+const txExplorer = useTxExplorer()
 function openInMempool(txHash: string) {
-  // Overlay the explorer above the current page — never navigate away.
-  useAppLauncherStore().openSession('mempool', { path: `/tx/${txHash}` })
+  // Local Mempool app when running; external explorer with consent
+  // otherwise (pruned nodes can't run Mempool).
+  txExplorer.openTx(txHash)
 }
 </script>