Add Advanced CSS editor to Initializr theme customization

[shai-almog]

Motivation

• Enable direct editing of CSS in the Initializr theme section so users can author CSS (using the new MutableResource + CSSThemeCompiler flow) and see live UI preview updates in the initializer preview pane.

Description

• Add ThemeEditorMode and customCss to ProjectOptions and thread editor mode and CSS through the initializer state model so options include editor mode and CSS content (scripts/initializr/common/src/main/java/com/codename1/initializr/model/ProjectOptions.java).
• Extend the Theme Customization panel in the Initializr UI to present an Editor toggle (SIMPLE / ADVANCED), keep existing controls in simple mode, and show a multiline CSS TextArea with a starter stylesheet in advanced mode (scripts/initializr/common/src/main/java/com/codename1/initializr/Initializr.java).
• Wire the live preview to compile and apply the user CSS at preview time by resetting the base theme and compiling the CSS with CSSThemeCompiler into a MutableResource, then merging parsed theme props into UIManager with addThemeProps so changes are reflected in the preview (scripts/initializr/common/src/main/java/com/codename1/initializr/ui/TemplatePreviewPanel.java).

Testing

• Tried cd scripts/initializr && ./mvnw -pl common test -DskipTests=false which failed in this environment due to network error while the Maven wrapper attempted to download the Maven distribution (java.net.SocketException: Network is unreachable).
• Tried offline compile with system Maven: cd scripts/initializr && mvn -pl common -DskipTests compile -o which failed because required plugin artifacts were not available in the local cache (missing maven-antrun-plugin:3.1.0).
• Attempted an automated UI screenshot via Playwright to validate the running Initializr preview, but there was no local server responding at http://localhost:8080 so the screenshot attempt returned net::ERR_EMPTY_RESPONSE.

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Codex Task

[github-actions]

Cloudflare Preview

• URL: https://pr-4580-website-preview.codenameone.pages.dev
• Branch: pr-4580-website-preview