Add localization support and preview to Initializr (bundles, UI, generator)

[shai-almog]

Motivation

• Provide built-in i18n support for generated starter projects by including message bundles and bootstrapping code for Barebones/Kotlin templates.
• Allow users to enable/disable inclusion of resource bundles and choose a preview language from the Initializr UI for live previews.
• Ensure the embedded live preview renders localized strings and that generated zips contain the correct resource files and bootstrap code.

Description

• Add PreviewLanguage enum and two fields to ProjectOptions: includeLocalizationBundles and previewLanguage, and wire them into defaults.
• Add a "Localization" panel to Initializr with a CheckBox to include bundles and a Picker to choose preview language, and pass those options through to the preview and generator.
• Update TemplatePreviewPanel to install the selected localization bundle into UIManager for live previews and to look up L10N resources by language suffix (with fallback for region variants).
• Update GeneratorModel to include messages*.properties files in the generated zip for Barebones templates (and only when enabled), and inject Java/Kotlin bootstrap code into the main source to load the messages bundle at runtime.
• Add localized messages.properties resource files for multiple languages (including RTL markers for Arabic/Hebrew) and update the summary and validation UI to reflect localization options.
• Update GeneratorModelMatrixTest to assert presence (or absence) of localization bundles in generated outputs for the relevant templates.

Testing

• Ran the module unit tests including the updated GeneratorModelMatrixTest which validates generated zip contents; tests passed.
• Built the initializr common module and executed the preview code path manually to confirm UIManager bundle installation and that generated zips contain common/src/main/resources/messages*.properties and injected bootstrap code in Barebones/Kotlin mains.

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Codex Task

[github-actions]

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