feat(lightning): channel open fee control, channels tab in wallet settings, mempool tx link

- Fee selector on channel open: Standard (~6 blocks) / Medium (~3) /
  Fast (next block) presets, or custom target confirmations / sat/vB;
  backend validates and passes target_conf / sat_per_vbyte to LND
- Extract channel management into LightningChannelsPanel, reused by the
  LND channels page and a new Channels tab in the Wallet Settings modal
- Funding tx link on each channel card opens the node's mempool app at
  /tx/<txid>

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

neode-ui/src/components/WalletSettingsModal.vue

@@ -11,6 +11,17 @@
       >{{ tab.label }}</button>
     </div>
 
+    <!-- ===================== Lightning Channels ===================== -->
+    <div v-show="activeTab === 'channels'">
+      <p class="text-white/60 text-sm mb-4">
+        Lightning channels on this node. Open a channel to a peer to send and receive Lightning payments.
+      </p>
+      <LightningChannelsPanel v-if="show" compact />
+      <div class="flex gap-3 mt-4">
+        <button @click="close" class="flex-1 glass-button px-4 py-2 rounded-lg text-sm">{{ t('common.close') }}</button>
+      </div>
+    </div>
+
     <!-- ===================== Cashu Mints ===================== -->
     <div v-show="activeTab === 'cashu'">
       <p class="text-white/60 text-sm mb-4">
@@ -145,6 +156,7 @@ import { ref, watch } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { rpcClient } from '@/api/rpc-client'
 import BaseModal from '@/components/BaseModal.vue'
+import LightningChannelsPanel from '@/components/LightningChannelsPanel.vue'
 
 const { t } = useI18n()
 
@@ -152,10 +164,11 @@ const props = defineProps<{ show: boolean }>()
 const emit = defineEmits<{ close: []; changed: [] }>()
 
 const tabs = [
+  { key: 'channels' as const, label: 'Channels' },
   { key: 'cashu' as const, label: 'Cashu Mints' },
   { key: 'fedimint' as const, label: 'Fedimint Federations' },
 ]
-const activeTab = ref<'cashu' | 'fedimint'>('cashu')
+const activeTab = ref<'channels' | 'cashu' | 'fedimint'>('channels')
 
 // Backed by wallet.fedimint-list / -join / -leave (fedimint-clientd HTTP bridge).
 // Join degrades gracefully with a clear error if the Fedimint client app isn't installed.