fix: route metadata through toolkit-lib

[mrgrain]

The cdk metadata command now delegates synthesis and single-stack selection to the existing toolkit-lib Toolkit.list() action instead of maintaining a separate legacy selection path. This keeps the CLI thin while preserving the command's YAML and --json output.

CliIoHost listeners can now override an effective message action, allowing the structured list result to remain tagged as metadata; matching and telemetry continue to use the originally emitted action. Focused IO snapshots protect both output formats and listener tests cover emitted-versus-effective action behavior.

Validation: yarn compile, yarn eslint, and focused Jest coverage for the metadata command, CliIoHost, and IoHostRecorder (90 tests).

Checklist

• Unit tests added/updated
• Integration tests added/updated (not required; no AWS interaction changed)
• No manual edits to generated files
• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
  • Release notes for the new version: N/A

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[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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