Update starter kit to use built-in TypeScript.

[harmony7]

To match the built-in TypeScript story we are updating the starter kit:

• Feeds index.ts directly to the js-compute-runtime compiler
• Now uses tsc in --noEmit mode to perform type checking only
• Updates README
• Includes updated tsconfig.json, including erasableSyntaxOnly

[Copilot]

Pull Request Overview

This PR updates the starter kit to use Fastly's built-in TypeScript support instead of requiring a separate TypeScript compilation step. The key change is feeding TypeScript source files directly to the js-compute-runtime compiler while using tsc only for type checking.

• Updates build process to feed index.ts directly to js-compute-runtime instead of compiling to JS first
• Changes TypeScript usage to type-checking only mode with tsc --noEmit
• Updates documentation to reflect the new TypeScript workflow

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
package.json	Updates build scripts and CLI version to support direct TypeScript compilation
fastly.toml	Updates description to clarify this is a TypeScript starter kit
README.md	Adds TypeScript feature documentation and explains the new built-in TypeScript workflow

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