feat(ui): dual-ecash wallet settings, buy-peer-files, seed backup, assorted fixes

- Tabbed Wallet Settings modal (Cashu + Fedimint) and dual-balance wallet card
- Buy a peer's paid file (ecash / node Lightning / on-chain / external QR)
- Recovery-phrase reveal + backup section; onboarding seed retry resilience
- NetBird HTTPS launch, remote-control two-finger scroll + external-open
- Shared BackButton, single-v version label, mesh Bitcoin header toggles

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/views/federation/FederationHeader.vue

@@ -1,25 +1,6 @@
 <template>
   <div class="mb-6">
-    <button
-      @click="router.push('/dashboard/web5')"
-      class="hidden md:flex items-center gap-2 text-white/70 hover:text-white transition-colors mb-4"
-    >
-      <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-        <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7" />
-      </svg>
-      Web5
-    </button>
-    <Teleport to="body">
-      <button
-        @click="router.push('/dashboard/web5')"
-        class="md:hidden mobile-back-btn glass-button px-6 py-3 rounded-lg font-medium shadow-2xl flex items-center justify-center gap-2"
-      >
-        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7" />
-        </svg>
-        <span>Web5</span>
-      </button>
-    </Teleport>
+    <BackButton label="Web5" @click="router.push('/dashboard/web5')" />
     <div class="flex items-start justify-between gap-4">
       <div>
         <h1 class="text-3xl font-bold text-white mb-2">Federation & Peers</h1>
@@ -52,6 +33,7 @@
 <script setup lang="ts">
 import { ref, computed } from 'vue'
 import { useRouter } from 'vue-router'
+import BackButton from '@/components/BackButton.vue'
 import { shortDid } from './utils'
 import { safeClipboardWrite } from '../web5/utils'