feat(@angular/cli): add initial set of signal form examples

[clydin]

This commit introduces a comprehensive set of 18 examples for the new signal-based forms functionality in Angular. These examples are designed to be used with the find_examples tool (MCP) to provide developers with actionable, real-world code snippets covering a wide range of use cases.

The find_examples tool is currently experimental and must be enabled using the -E find_examples option when running the ng mcp command.

The examples cover the following key concepts:

• Core concepts and basic setup
• Built-in and cross-field validation
• Dynamic and conditional form structures
• Custom form controls and reusable validators
• Asynchronous operations and third-party integrations (Zod)
• Best practices for testing, accessibility, and styling