feat(wallet-ui): Ark send/receive tabs + Ark pay-with option on peer files

Send modal gains an Ark tab (address/invoice/lightning-address via
wallet.ark-send), Receive gains an Ark address + QR tab, and the peer
file purchase confirm offers Ark alongside Cashu/Fedimint. Demo mock
exposes ark_sats in wallet.ecash-balance and deducts the chosen rail on
paid downloads.

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

neode-ui/src/components/ReceiveBitcoinModal.vue

@@ -3,12 +3,12 @@
         <!-- Method tabs -->
         <div class="flex gap-1 mb-4 p-1 bg-white/5 rounded-lg">
           <button
-            v-for="m in (['onchain', 'lightning', 'ecash'] as const)"
+            v-for="m in (['onchain', 'lightning', 'ecash', 'ark'] as const)"
             :key="m"
             @click="receiveMethod = m"
             class="flex-1 px-2 py-1.5 rounded text-xs font-medium capitalize transition-colors"
             :class="receiveMethod === m ? 'bg-white/15 text-white' : 'text-white/50 hover:text-white/80'"
-          >{{ m === 'onchain' ? t('receiveBitcoin.onChain') : m === 'lightning' ? t('receiveBitcoin.lightning') : t('receiveBitcoin.ecash') }}</button>
+          >{{ m === 'onchain' ? t('receiveBitcoin.onChain') : m === 'lightning' ? t('receiveBitcoin.lightning') : m === 'ecash' ? t('receiveBitcoin.ecash') : 'Ark' }}</button>
         </div>
 
         <!-- Lightning -->
@@ -43,6 +43,19 @@
           </div>
         </div>
 
+        <!-- Ark -->
+        <div v-if="receiveMethod === 'ark'">
+          <div v-if="arkAddress" class="mb-3 p-3 bg-white/5 rounded-lg text-center">
+            <canvas ref="arkQrCanvas" class="mx-auto mb-3 rounded-lg" style="image-rendering: pixelated;"></canvas>
+            <p class="text-white/50 text-xs mb-2">Your Ark address</p>
+            <p class="text-sm font-mono text-white/90 break-all">{{ arkAddress }}</p>
+            <button @click="copyText(arkAddress)" class="mt-2 text-xs text-orange-400 hover:text-orange-300">{{ t('common.copy') }}</button>
+          </div>
+          <div v-else class="mb-3 text-center">
+            <p class="text-white/50 text-sm mb-2">Generate a fresh Ark address to receive off-chain sats instantly.</p>
+          </div>
+        </div>
+
         <!-- Ecash -->
         <div v-if="receiveMethod === 'ecash'">
           <div class="mb-3">
@@ -57,7 +70,7 @@
         <div class="flex gap-3">
           <button @click="close" class="flex-1 glass-button px-4 py-2 rounded-lg text-sm">{{ t('common.close') }}</button>
           <button @click="receive" :disabled="processing" class="flex-1 glass-button glass-button-success px-4 py-2 rounded-lg text-sm font-medium disabled:opacity-50">
-            {{ processing ? t('receiveBitcoin.processing') : receiveMethod === 'onchain' ? t('receiveBitcoin.generateAddress') : receiveMethod === 'lightning' ? t('receiveBitcoin.createInvoice') : t('receiveBitcoin.receive') }}
+            {{ processing ? t('receiveBitcoin.processing') : receiveMethod === 'onchain' ? t('receiveBitcoin.generateAddress') : receiveMethod === 'lightning' ? t('receiveBitcoin.createInvoice') : receiveMethod === 'ark' ? 'Get Ark address' : t('receiveBitcoin.receive') }}
           </button>
         </div>
   </BaseModal>
@@ -75,15 +88,17 @@ const { t } = useI18n()
 defineProps<{ show: boolean }>()
 const emit = defineEmits<{ close: []; received: [] }>()
 
-const receiveMethod = ref<'lightning' | 'onchain' | 'ecash'>('onchain')
+const receiveMethod = ref<'lightning' | 'onchain' | 'ecash' | 'ark'>('onchain')
 const invoiceAmount = ref<number>(0)
 const invoiceMemo = ref('')
 const invoiceResult = ref('')
 const onchainAddress = ref('')
+const arkAddress = ref('')
 const ecashToken = ref('')
 const ecashResult = ref('')
 const onchainQrCanvas = ref<HTMLCanvasElement | null>(null)
 const lightningQrCanvas = ref<HTMLCanvasElement | null>(null)
+const arkQrCanvas = ref<HTMLCanvasElement | null>(null)
 const processing = ref(false)
 const error = ref('')
 
@@ -102,6 +117,7 @@ async function renderQr(data: string, canvas: HTMLCanvasElement | null, prefix =
 function close() {
   invoiceResult.value = ''
   onchainAddress.value = ''
+  arkAddress.value = ''
   ecashToken.value = ''
   ecashResult.value = ''
   error.value = ''
@@ -131,6 +147,11 @@ async function receive() {
       }
       onchainAddress.value = res.address
       nextTick(() => renderQr(res.address, onchainQrCanvas.value, 'bitcoin:'))
+    } else if (receiveMethod.value === 'ark') {
+      const res = await rpcClient.call<{ address: string }>({ method: 'wallet.ark-address' })
+      if (!res.address) throw new Error('barkd did not return an Ark address')
+      arkAddress.value = res.address
+      nextTick(() => renderQr(res.address, arkQrCanvas.value))
     } else {
       if (!ecashToken.value.trim()) { error.value = t('receiveBitcoin.pasteAnEcashToken'); return }
       // The backend auto-detects the token type: a Cashu token (cashuA/B…) is