feat(lightning): instant pay feedback, balances never vanish mid-payment

Framework-pt report: a paid invoice stalled the UI with no success
shown, and lightning/total balances disappeared until it settled.
Three compounding causes, three fixes:

- Backend payinvoice's synchronous wait drops 120s → 8s. Fast payments
  (the majority) still settle in one round trip; slow multi-hop routes
  return pending + payment_hash quickly and the caller's 3s poll takes
  over — instead of the modal freezing for up to two minutes.
- payLightningInvoice gains an onPending hook: SendBitcoinModal and the
  scan modal now flip to a visible "Settling…" success pane the moment
  the payment goes pending (safe to close), and the ongoing poll
  upgrades it to Paid — or replaces it with LND's real failure.
- One slow lnd.getinfo poll (5s budget) flipped the Home wallet card to
  "disconnected", hiding balances the user already knew. Three
  consecutive failures are now required (~30s) before the card gives up;
  last-known balances keep rendering throughout.

rpc-client tests 75/75.

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

neode-ui/src/components/WalletScanModal.vue

@@ -704,8 +704,18 @@ async function confirmSend() {
       const params: { payment_request: string; amount_sats?: number } = { payment_request: dest.value }
       if (!amountLocked.value && effectiveAmount.value > 0) params.amount_sats = effectiveAmount.value
       // Waits out slow multi-hop routing and only reports failure when LND
-      // itself declares the payment failed — never on a timeout.
-      const res = await rpcClient.payLightningInvoice(params)
+      // itself declares the payment failed — never on a timeout. Pending
+      // (~8s) jumps straight to the success pane in SETTLING mode instead of
+      // spinning through the whole poll; the poll upgrades it to PAID.
+      const res = await rpcClient.payLightningInvoice(params, (hash) => {
+        successAmount.value = effectiveAmount.value
+        successVerb.value = 'SETTLING'
+        successDetail.value = 'Payment is on its way — this updates the moment it settles. Safe to close.'
+        successRef.value = hash
+        processing.value = false
+        goTo('success')
+        emit('sent')
+      })
       if (res.status === 'failed') throw new Error(res.failure_reason || 'Payment failed')
       successAmount.value = res.amount_sats || effectiveAmount.value
       successVerb.value = res.status === 'pending' ? 'SENDING' : 'PAID'