[camera_android_camerax] Migrate from dart_skills_lint to skills_lint

[reidbaker-agent]

The skills_lint code is moving out of flutter/agent-plugins to its own github repo skills_lint.dart.
-@reidbaker

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Relevant prompts

ok our task today is to migrate (and document how to migrate) the use of dart_skills_lint in the package repo to skills_lint.dart. 

Feel free to ask me questions  

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Agent authored description
Migrates camera_android_camerax from the legacy dart_skills_lint dependency to skills_lint from google/skills_lint.dart pinned to commit hash e6e695e1550f81342fe5acd4dbe65040b5aa44c3.

• Renames dart_skills_lint.yaml to skills_lint.yaml and updates root key to skills_lint:.
• Updates Dart imports in test/validate_skills_test.dart and test/enforce_tracked_skills_prevent_publishing_rule.dart to package:skills_lint/skills_lint.dart.
• Updates diagnostic messages and skill documentation references.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I updated/added any relevant documentation (doc comments with ///).
• All existing and new tests are passing.