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>

core/archipelago/src/api/rpc/lnd/payments.rs

@@ -74,14 +74,18 @@ impl RpcHandler {
         // payment settles or definitively fails, and multi-hop routing with
         // retries routinely takes longer than the shared client's 15s budget.
         // That 15s abort used to surface as "Payment failed" while LND kept
-        // paying in the background — the payment then succeeded and appeared
-        // in history a minute later. Wait up to 120s on a dedicated client,
-        // and treat a post-connect timeout as IN FLIGHT (status: pending),
-        // never as failure — only LND may declare a payment failed.
+        // paying in the background — only LND may declare a payment failed,
+        // so a post-connect timeout is IN FLIGHT (status: pending), never
+        // failure. The window is deliberately SHORT: most payments settle in
+        // a couple of seconds and still get their answer in one round trip,
+        // while a slow multi-hop route flips the UI into its "settling…"
+        // polling state (lnd.paymentstatus every 3s) after ~8s instead of
+        // freezing the modal for two minutes with no feedback (framework-pt
+        // user report, 2026-07-29).
         let pay_client = reqwest::Client::builder()
             .no_proxy()
             .connect_timeout(std::time::Duration::from_secs(10))
-            .timeout(std::time::Duration::from_secs(120))
+            .timeout(std::time::Duration::from_secs(8))
             .danger_accept_invalid_certs(true)
             .build()
             .context("Failed to create HTTP client")?;