Keep Initializr loader visible until CN1 UI ready

[shai-almog]

Motivation

• Prevent the visual switch from the modern website loader to the older app icon/progress UI by keeping the single loader style active until the embedded CN1 Initializr app actually displays its first form.
• Provide a reliable handshake so web wrapper pages know when the CN1 UI is ready and avoid premature dismissal of the overlay.

Description

• The website loader logic in docs/website/layouts/_default/initializr.html now waits for a postMessage with type cn1-initializr-ui-ready or an 8s iframe-load fallback before hiding the overlay instead of hiding immediately on iframe.load.
• Added a new notifyUiReady() method to the WebsiteThemeNative interface in scripts/initializr/common/src/main/java/com/codename1/initializr/WebsiteThemeNative.java.
• Call notifyWebsiteUiReady() (which invokes the native bridge) immediately after form.show() in scripts/initializr/common/src/main/java/com/codename1/initializr/Initializr.java so the parent page receives the ready signal as soon as the CN1 form is visible.
• Implemented the JS native bridge notifyUiReady_ in scripts/initializr/javascript/src/main/javascript/com_codename1_initializr_WebsiteThemeNative.js to postMessage() the readiness event to the parent page.

Testing

• Attempted to compile/run the Initializr common module with Maven using mvn -f scripts/initializr/pom.xml -pl common -am -DskipTests compile, which progressed but failed during an Ant task that downloads UpdateCodenameOne.jar due to network unreachability in this environment (build failed with java.net.SocketException: Network is unreachable).
• Also tried ./mvnw -pl common test -DskipITs and mvn -f scripts/initializr/pom.xml -pl common -DskipTests compile -o; these failed due to wrapper/network/offline plugin resolution issues in this environment, so runtime validation on a live page was not possible here.
• Git changes were staged and committed locally (Keep Initializr loader style consistent until UI is ready).

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Codex Task

[github-actions]

Cloudflare Preview

• URL: https://pr-4576-website-preview.codenameone.pages.dev
• Branch: pr-4576-website-preview