Improve skill for using dart_skills_lint

[reidbaker]

Add information for initial setup based on real world integrations into flutter/flutter and devtools
Add package skills to evaluation set

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request updates the dart_skills_lint configuration and significantly expands the SKILL.md documentation, adding a detailed test example with logging and a new section on integration best practices. Feedback highlights a configuration error where directory-specific rules must be nested under a 'rules' key to be recognized. Additionally, it is suggested to clarify that generated baseline files require an explicit reference in the YAML configuration to be active.