Clarify Quick Start terminology for frontmatter and .lock.yml

[Copilot]

Quick Start used two terms without defining them on first use: frontmatter and .lock.yml. This tightens the onboarding copy so beginners can understand the file structure and generated workflow artifacts without leaving the page.

• Quick Start wording

  • Defines frontmatter inline as the settings block between the --- lines.
  • Defines .lock.yml inline in Step 2 as the compiled workflow that GitHub Actions runs.

• Scope

  • Limits the change to the first-use explanations in docs/src/content/docs/setup/quick-start.mdx.
  • Keeps the existing flow and deeper reference links unchanged.

Example of the updated clarification:

> Note: if `engine:` is later removed manually from the workflow frontmatter
> (the settings block at the top of the file, between the `---` lines),
> the runtime defaults to Copilot.

4. **Add the workflow** - Adds the workflow file (`.md`) and its generated
GitHub Actions lock file (`.lock.yml`, the compiled workflow that GitHub Actions
actually runs) to `.github/workflows/`.

[Copilot]

Pull request overview

Updates the Quick Start documentation to define “frontmatter” and “.lock.yml” inline on first mention, improving onboarding clarity for new users reading the gh aw setup guide.

Changes:

• Clarifies “frontmatter” as the settings block between the --- lines at the top of the workflow file.
• Clarifies “.lock.yml” as the compiled GitHub Actions workflow that actually runs.

Show a summary per file

File	Description
docs/src/content/docs/setup/quick-start.mdx	Adds first-use definitions for frontmatter and .lock.yml within the Quick Start flow.

Review details

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• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Low

[github-actions]

🎉 This pull request is included in a new release.

Release: v0.82.4