Expand existing tool format detection

[andrew]

Several existing knowledge definitions omit files that can identify their tools. The generated README introduction also embeds knowledge-base totals, which become stale whenever tool definitions change.

• Add Gradle version-catalog detection for libs.versions.toml.
• Add NuGet central package management detection for Directory.Packages.props and Directory.Build.props.
• Add Helm support for Chart.lock, requirements.yaml, and requirements.lock.
• Add Yarn Plug'n'Play detection for .pnp.cjs.
• Add legacy pnpm lockfile detection for shrinkwrap.yaml.
• Add Ansible Galaxy detection for requirements.yml, requirements.yaml, galaxy.yml, and galaxy.yaml.
• Add plain BUILD detection to the Bazel definition without conflicting with Pants.
• Remove numeric knowledge-base totals from listToolsReadme.
• Regenerate the README tool block with a count-free introduction.

Each detection change should include a focused fixture or unit test.