Update Angular starters to Angular v21

[hawkgs]

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[gemini-code-assist]

Summary of Changes

Hello @hawkgs, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on a significant upgrade of the Angular starter projects to version 21. The update encompasses core framework dependencies, build tools, and TypeScript, ensuring these starters leverage the latest Angular ecosystem. Additionally, it introduces explicit change detection providers for server-side rendering, with a specific adoption of zoneless change detection in the dashboard starter, and enhances the AI chatbot's capabilities by upgrading its underlying Gemini model.

Highlights

• Angular Version Upgrade: All Angular starter projects have been updated from Angular v20 to Angular v21, including core Angular packages, CLI, build tools, and compiler-cli. This ensures compatibility with the latest framework features and improvements.
• TypeScript Version Update: The TypeScript dependency across all updated starter projects has been upgraded from ~5.8.3 to ~5.9.3.
• Change Detection Strategy Updates: The server-side rendering (SSR) bootstrap process in most Angular starters (ai-chatbot, ai-text-editor, ecommerce, image-gallery, kanban) now explicitly includes provideZoneChangeDetection() in their providers. The ecommerce starter also applies this to its client-side main.ts.
• Zoneless Change Detection in Dashboard: The dashboard Angular starter has been updated to use provideZonelessChangeDetection() for its server-side rendering bootstrap, indicating a shift towards a more modern, zoneless change detection strategy for that specific project.
• Gemini Model Upgrade: The ai-chatbot starter project has upgraded its Gemini AI model from gemini-1.5-flash to gemini-2.5-flash for both direct API calls and chat sessions, potentially offering improved AI capabilities.
• New Angular Build Dependency: A new development dependency, @angular/build, has been added to all updated package.json files, reflecting changes in Angular's build tooling.

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[gemini-code-assist]

Code Review

This pull request successfully updates the Angular starter projects to version 21. The changes primarily involve updating dependencies in package.json files and modifying the application bootstrap logic in main.server.ts and main.ts to align with the latest Angular APIs, including the new change detection providers. The Gemini model used in the AI chatbot starter has also been updated. The changes are consistent and look correct for the upgrade. I've added a couple of suggestions to improve maintainability in the AI chatbot's server code.