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/composables/useTxExplorer.ts

@@ -0,0 +1,106 @@
+// Shared "open this transaction in an explorer" logic (2026-07-22).
+//
+// Nodes with a PRUNED bitcoin node can't run the Mempool app at all, but the
+// wallet UI's tx links used to blindly open the local app anyway (blank app
+// frame). Routing:
+//   - local Mempool app running  → open it, exactly as before
+//   - otherwise                  → an EXTERNAL explorer, after a one-time
+//     consent modal: viewing a tx on someone else's mempool tells that
+//     server's operator which transaction you're interested in (plus your
+//     IP), so the user must knowingly opt in and may point the link at
+//     their own trusted instance instead.
+//
+// Preference + acknowledgement persist per browser in localStorage
+// (`archipelago.tx-explorer.v1`); the Settings → System section edits the
+// same values.
+import { ref } from 'vue'
+import { useAppLauncherStore } from '@/stores/appLauncher'
+import { useContainerStore } from '@/stores/container'
+
+export const DEFAULT_TX_EXPLORER = 'https://tx1138.com'
+export const EXPLORER_PLACEHOLDER = 'https://mempool.guide'
+
+const KEY = 'archipelago.tx-explorer.v1'
+
+interface TxExplorerPrefs {
+  url: string
+  acknowledged: boolean
+}
+
+function loadPrefs(): TxExplorerPrefs {
+  const defaults: TxExplorerPrefs = { url: DEFAULT_TX_EXPLORER, acknowledged: false }
+  try {
+    return { ...defaults, ...JSON.parse(localStorage.getItem(KEY) || '{}') }
+  } catch {
+    return defaults
+  }
+}
+
+// Module-scope state: one source of truth shared by every caller, the global
+// consent modal, and the Settings section.
+const prefs = ref<TxExplorerPrefs>(loadPrefs())
+/** Tx hash awaiting user consent — non-null shows ExternalExplorerModal. */
+const pendingTx = ref<string | null>(null)
+
+function savePrefs() {
+  localStorage.setItem(KEY, JSON.stringify(prefs.value))
+}
+
+export function useTxExplorer() {
+  const launcher = useAppLauncherStore()
+  const containers = useContainerStore()
+
+  /** Normalized explorer base URL (no trailing slash). */
+  function explorerUrl(): string {
+    return (prefs.value.url || DEFAULT_TX_EXPLORER).trim().replace(/\/+$/, '')
+  }
+
+  function openExternal(txHash: string) {
+    window.open(`${explorerUrl()}/tx/${txHash}`, '_blank', 'noopener,noreferrer')
+  }
+
+  /** Entry point for every "view transaction" affordance in the app. */
+  function openTx(txHash: string) {
+    if (containers.getAppState('mempool') === 'running') {
+      launcher.openSession('mempool', { path: `/tx/${txHash}` })
+      return
+    }
+    if (prefs.value.acknowledged) {
+      openExternal(txHash)
+      return
+    }
+    pendingTx.value = txHash
+  }
+
+  /** Consent modal confirm: persist the (possibly edited) URL + ack, open. */
+  function confirmPending(url: string, dontAskAgain: boolean) {
+    const trimmed = url.trim()
+    prefs.value.url = trimmed || DEFAULT_TX_EXPLORER
+    if (dontAskAgain) prefs.value.acknowledged = true
+    savePrefs()
+    const tx = pendingTx.value
+    pendingTx.value = null
+    if (tx) openExternal(tx)
+  }
+
+  function cancelPending() {
+    pendingTx.value = null
+  }
+
+  /** Settings hook: change the explorer and/or reset the consent. */
+  function setExplorer(url: string, acknowledged?: boolean) {
+    prefs.value.url = url.trim() || DEFAULT_TX_EXPLORER
+    if (acknowledged !== undefined) prefs.value.acknowledged = acknowledged
+    savePrefs()
+  }
+
+  return {
+    prefs,
+    pendingTx,
+    explorerUrl,
+    openTx,
+    confirmPending,
+    cancelPending,
+    setExplorer,
+  }
+}