fix(lightning): never report a slow in-flight payment as failed

Slow multi-hop payments (>15s routing) surfaced as "Payment failed"
while LND settled them in the background: the shared LND REST client's
15s total timeout aborted the synchronous /v1/channels/transactions
wait, and every UI path treated that abort as a definitive failure. The
payment then succeeded anyway and only appeared in history on the next
background poll.

Backend: lnd.payinvoice now decodes the invoice up front for its payment
hash, pays on a dedicated 120s client, and answers status:"pending" with
the hash (never an error) when the wait elapses after the payment was
handed to LND — only a pre-connect failure is still a hard error. New
lnd.paymentstatus RPC reports succeeded/failed/in_flight (with humanized
failure reasons) from /v1/payments.

Frontend: new rpcClient.payLightningInvoice() pays then polls
lnd.paymentstatus to a real terminal state (3s interval, up to 2 min);
all five call sites (send modal, scan modal, web5 unified send, peer-file
purchase, app-launcher payments) migrated. Failure is only shown when LND
itself declares FAILED; a still-settling payment shows an in-flight state
and success fires the transaction refresh.

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

neode-ui/src/views/PeerFiles.vue

@@ -1320,8 +1320,8 @@ async function payWithInvoice() {
 
 /**
  * Pay the seller's invoice straight from THIS node's Lightning wallet, then
- * release the file. No QR/polling: lnd.payinvoice only returns once the payment
- * settles, so the payment_hash is immediately valid as the download gate token.
+ * release the file. payLightningInvoice resolves to a real terminal state, so
+ * on success the payment_hash is immediately valid as the download gate token.
  */
 async function payWithLightning() {
   const item = payItem.value
@@ -1341,14 +1341,15 @@ async function payWithLightning() {
       lnError.value = inv?.error || 'The seller could not create an invoice (is its Lightning node running?).'
       return
     }
-    // 2. Pay it from our own node. Returns only after settlement.
-    const pay = await rpcClient.call<{ payment_hash?: string; payment_error?: string }>({
-      method: 'lnd.payinvoice',
-      params: { payment_request: inv.bolt11 },
-      timeout: 120000,
-    })
-    if (pay?.payment_error) {
-      lnError.value = `Payment failed: ${pay.payment_error}`
+    // 2. Pay it from our own node. Tracked to a REAL terminal state — a slow
+    // multi-hop route resolves via status polling instead of a false failure.
+    const pay = await rpcClient.payLightningInvoice({ payment_request: inv.bolt11 })
+    if (pay.status === 'failed') {
+      lnError.value = `Payment failed: ${pay.failure_reason || 'unknown reason'}`
+      return
+    }
+    if (pay.status === 'pending') {
+      lnError.value = 'Payment is still settling — this can take a few minutes. Check your wallet transactions before paying again.'
       return
     }
     // 3. Settled — pull the file using the payment hash as the gate token.