@sdk: Lazy-load wallet icons instead of preloading all

[jenshenJ]

Describe the bug

All wallet images are loaded eagerly when the SDK initializes.

Expected behavior

Use lightweight placeholders and load wallet images on demand when they become visible.

Current behavior

All wallet images load on DOMContentLoaded. Many icons are never shown; at ~100+ KB each, ~20 wallets adds roughly 2 MB of avoidable downloads.

Steps to Reproduce

1. Open a dApp on a mobile network with DevTools → Network open.
2. Load the page and observe image requests before opening the wallet modal.

Environment

web

Additional context

No response

[maxrihter]

Prepared a PR for this: kept the existing skeleton placeholder and added IntersectionObserver-based deferral in the shared Image component (150 px prefetch margin, with a fallback to the old eager behavior where IO is unavailable), and removed the constructor-time preload of the full wallets list.

Result: page load now fetches 0 wallet icons (was ~35 / ~2 MB); opening the modal fetches only the visible ones; the all-wallets list loads progressively on scroll. Covered with unit tests + checked on chromium/webkit/firefox.

Happy to adjust the approach if you had something else in mind — details and measurements in the PR.