feat(payments): payment-event dispatcher + the provider-return UX

Deliver payment_events to connected clients as an in-app wallet-refresh push: a
background dispatcher drains undispatched events and publishes a KindNotification
"payment" signal, marking each delivered; the client bumps a wallet-refresh
counter the open Wallet screen watches, re-fetching in place. A return-focus
refetch is the fallback. The Robokassa Success/Fail return now serves a
self-closing page (the payment opens in a separate window) so the customer drops
back into the live app instead of a cold start. Integration test for the event
drain/mark queue.

ui/src/lib/app.svelte.ts

@@ -137,6 +137,9 @@ export const app = $state<{
   /** Whether an operator feedback reply awaits the player, for the lobby ⚙️ badge (combined
    *  with friend requests) and the Settings → Info badge. */
   feedbackReplyUnread: boolean;
+  /** A monotone counter bumped when a payment-intake push signals the wallet changed; an open
+   *  Wallet screen watches it and re-fetches in place. */
+  walletRefresh: number;
   /** Whether to show the "outdated invite link" notice: set when a Telegram deep-link friend
    *  code is already used/expired, so the visitor lands in the lobby with a gentle pointer to
    *  the bot instead of a scary error on the Friends screen. */
@@ -175,6 +178,7 @@ export const app = $state<{
   chatUnread: {},
   messageUnread: {},
   feedbackReplyUnread: false,
+  walletRefresh: 0,
   staleInvite: false,
   welcomeRedeem: false,
   resync: 0,
@@ -439,6 +443,12 @@ function openStream(): void {
         if (e.sub === 'profile') {
           void refreshProfile();
         }
+        // A payment-intake event credited (or refunded) the viewer's wallet: bump the signal an
+        // open Wallet screen watches, so it re-fetches in place (the return-focus poll is the
+        // fallback when the live stream is down).
+        if (e.sub === 'payment') {
+          app.walletRefresh++;
+        }
         void refreshNotifications();
       }
     },