[ak-cipher]

Problem

On Flutter web, the splash <picture> stays in the page after the app is drawn. Chrome on Android can still long-press that hidden image. removeSplashFromWeb() only runs when the app calls FlutterNativeSplash.remove(), so the default setup never unloads it.

Fixes #815

Changes

• Unload each splash image (src / srcset) and remove #splash and #splash-branding when Flutter dispatches flutter-first-frame.
• Keep those images non-selectable while they are on screen.
• preserve() still holds the splash, because it delays that first frame until remove().

Verification

In the example app, with preserve() and remove() commented out:

• Before: document.getElementById("splash") returned the <picture>, currentSrc was splash/img/dark-2x.png, and the hit list was FLUTTER-VIEW, IMG, BODY, HTML.
• After regenerating web/index.html and reloading: document.getElementById("splash") was null, currentSrc was undefined, and the hit list was FLUTTER-VIEW, BODY, HTML.