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/SendBitcoinModal.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 (['auto', 'lightning', 'onchain', 'ecash'] as const)"
+            v-for="m in (['auto', 'lightning', 'onchain', 'ecash', 'ark'] as const)"
             :key="m"
             @click="sendMethod = m"
             class="flex-1 px-2 py-1.5 rounded text-xs font-medium capitalize transition-colors"
             :class="sendMethod === m ? 'bg-white/15 text-white' : 'text-white/50 hover:text-white/80'"
-          >{{ m === 'onchain' ? t('sendBitcoin.onChain') : m === 'lightning' ? t('sendBitcoin.lightning') : m === 'ecash' ? t('sendBitcoin.ecash') : t('sendBitcoin.auto') }}</button>
+          >{{ m === 'onchain' ? t('sendBitcoin.onChain') : m === 'lightning' ? t('sendBitcoin.lightning') : m === 'ecash' ? t('sendBitcoin.ecash') : m === 'ark' ? 'Ark' : t('sendBitcoin.auto') }}</button>
         </div>
 
         <div v-if="sendMethod === 'auto'" class="mb-3 p-2 bg-white/5 rounded-lg">
@@ -22,9 +22,9 @@
 
         <div v-if="effectiveMethod !== 'ecash'" class="mb-3">
           <label class="text-white/60 text-sm block mb-1">
-            {{ effectiveMethod === 'lightning' ? t('sendBitcoin.lightningInvoice') : t('sendBitcoin.bitcoinAddress') }}
+            {{ effectiveMethod === 'lightning' ? t('sendBitcoin.lightningInvoice') : effectiveMethod === 'ark' ? 'Ark address, invoice or lightning address' : t('sendBitcoin.bitcoinAddress') }}
           </label>
-          <textarea v-model="dest" rows="2" :placeholder="effectiveMethod === 'lightning' ? 'lnbc...' : 'bc1...'" class="w-full input-glass font-mono"></textarea>
+          <textarea v-model="dest" rows="2" :placeholder="effectiveMethod === 'lightning' ? 'lnbc...' : effectiveMethod === 'ark' ? 'tark1… / lnbc… / user@lnaddress' : 'bc1...'" class="w-full input-glass font-mono"></textarea>
         </div>
 
         <div v-if="ecashToken && effectiveMethod === 'ecash'" class="mb-3 p-2 bg-white/5 rounded-lg">
@@ -39,6 +39,9 @@
         <div v-if="resultHash" class="mb-3 alert-success">
           <p class="text-xs">{{ t('sendBitcoin.paidHash', { hash: resultHash }) }}</p>
         </div>
+        <div v-if="resultArk" class="mb-3 alert-success">
+          <p class="text-xs">{{ resultArk }}</p>
+        </div>
 
         <div v-if="error" class="mb-3 alert-error">{{ error }}</div>
 
@@ -62,13 +65,14 @@ const { t } = useI18n()
 const props = defineProps<{ show: boolean }>()
 const emit = defineEmits<{ close: []; sent: [] }>()
 
-const sendMethod = ref<'auto' | 'lightning' | 'onchain' | 'ecash'>('auto')
+const sendMethod = ref<'auto' | 'lightning' | 'onchain' | 'ecash' | 'ark'>('auto')
 const amount = ref<number>(0)
 const dest = ref('')
 const processing = ref(false)
 const error = ref('')
 const resultTxid = ref('')
 const resultHash = ref('')
+const resultArk = ref('')
 const ecashToken = ref('')
 
 const effectiveMethod = computed(() => {
@@ -84,6 +88,7 @@ function close() {
   error.value = ''
   resultTxid.value = ''
   resultHash.value = ''
+  resultArk.value = ''
   ecashToken.value = ''
   emit('close')
 }
@@ -99,10 +104,20 @@ async function send() {
   ecashToken.value = ''
   resultTxid.value = ''
   resultHash.value = ''
+  resultArk.value = ''
 
   const method = effectiveMethod.value
   try {
-    if (method === 'ecash') {
+    if (method === 'ark') {
+      if (!dest.value.trim()) { error.value = 'Enter an Ark address, invoice or lightning address'; return }
+      await rpcClient.call<{ sent: boolean }>({
+        method: 'wallet.ark-send',
+        params: { destination: dest.value.trim(), amount_sats: amount.value },
+        // Ark sends can wait on round participation.
+        timeout: 130000,
+      })
+      resultArk.value = `Sent ${amount.value.toLocaleString()} sats via Ark`
+    } else if (method === 'ecash') {
       const res = await rpcClient.call<{ token: string }>({
         method: 'wallet.ecash-send',
         params: { amount_sats: amount.value },