Remove unused dart_code_linter dependency and dead rules config

[reidbaker-agent]

I should have caught this in #211 but I thought the analyzer warnings were running an action step.

• @reidbaker

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Relevant prompts

Double check that dart_code_linter was giving me a false sense of safety if nothing was running the analyzer checks that are defined.
ok cut a pr from the recently updated main and remove that package and any references to it. Open a pr and have the pr description lay out why this code was giving a false sense of security.

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Agent authored pr description

Summary

Removes package:dart_code_linter from pubspec.yaml and deletes dead dart_code_linter: rules configuration from analysis_options.yaml.

Motivation and Context

dart_code_linter was declared as a dev_dependency in pubspec.yaml and had 15 custom rules configured in analysis_options.yaml. However, this package was creating a false sense of security because none of its rules were actually being executed in development or CI.

Why this code was giving a false sense of security:

1. Unregistered as an Analyzer Plugin: dart_code_linter was intentionally omitted from analyzer: plugins: in analysis_options.yaml (due to racy false positives documented in issue Flaky CI: analyze_and_test (windows-latest) intermittently fails on `dart analyze --fatal-infos #144). Consequently, standard dart analyze ignores the dart_code_linter: block entirely and only runs standard Dart SDK lints.
2. Never Executed via CLI: To run dart_code_linter rules without an analyzer plugin, the CLI command dart run dart_code_linter:metrics analyze lib test must be invoked. This command was never called in .github/workflows/, pre-commit hooks, or developer verification scripts. (Note: CI's cognitive_complexity check uses package:cognitive_complexity, a separate single-purpose tool).

Removing this unused dependency cleans up dead configuration and removes an unmaintained dev dependency.

Related Issues

N/A

What changed

• tool/dart_skills_lint/pubspec.yaml: Removed dart_code_linter: ^4.0.3 from dev_dependencies.
• tool/dart_skills_lint/analysis_options.yaml: Removed the dead dart_code_linter: configuration section and the accompanying comment explaining why it was omitted from analyzer plugins.

Testing Instructions

• Run dart format . to verify formatting.
• Run dart analyze --fatal-infos to verify static analysis.
• Run dart run cognitive_complexity --fail-threshold 48 tool/dart_skills_lint/lib tool/dart_skills_lint/test to verify complexity metrics.
• Run dart test to verify unit tests.
• Run dart run bin/cli.dart -d .agents/skills to validate repository skills.

[gemini-code-assist]

Code Review

This pull request removes the dart_code_linter dependency and its configuration from pubspec.yaml and analysis_options.yaml. Feedback was provided regarding a missing trailing newline at the end of analysis_options.yaml to ensure compatibility and prevent Git warnings.