Add next steps guidance to learning pathway

[MuthuGCodes]

Description

Fixes #13530

• Adds a "Ready to start" CTA on the learning pathway landing page linking to Step 1.
• Adds /learn/pathway/tutorial to tutorial.yml so next/previous step navigation flows sequentially through the tutorial introduction.

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks of 80 characters or fewer.

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit d2639d3):

https://flutter-docs-prod--docs-pr13697-issue-13530-oe8yzcm8.web.app

[flutter-website-bot]

Staged preview of the updated flutter.dev site (updated for commit d2639d3):

https://flutter-dev-230821--www-pr13697-issue-13530-zpe5vt6h.web.app

[sfshaza2]

I know this is a draft, but lgtm

[gemini-code-assist]

Code Review

This pull request adds a "Ready to start?" section with a quick install link to the pathway index documentation, and introduces a "Tutorial introduction" chapter to the tutorial configuration. Feedback was provided to apply semantic line breaks to the newly added documentation text to improve diff readability.

[gemini-code-assist]

To adhere to the semantic line breaks guidelines, consider splitting this sentence at a logical boundary (such as the conjunction 'and'). This keeps lines shorter and makes future diffs cleaner.

Suggested change

	Get started by installing Flutter and setting up your development environment:
	Get started by installing Flutter
	and setting up your development environment:

References

1. Use semantic line breaks: split long sentences at logical boundaries, such as conjunctions, to keep lines short and clean in diffs. ^(link)