Define Gradle version catalog inspection approach

[JuanTorchia]

Summary

• Add a design note for read-only Gradle version catalog inspection without executing Gradle.
• Define the MVP scope: conventional gradle/libs.versions.toml, TOML parsing, alias normalization, dependency/plugin alias resolution, and bundle expansion.
• Document out-of-scope areas: custom catalogs, convention plugins, dynamic aliases, conflict resolution, and effective version calculation.
• Link the proposal from the rule contribution guide.

Validation

• python -B scripts/check-local-markdown-links.py
• Legacy documentation path search returns only the historical rename note in docs/engineering-log/012-public-repository-readiness.md.
• Public documentation hygiene search returns no workstation-specific paths or private planning references.
• git diff --check
• mvn clean test '-Dmaven.compiler.release=22'

Closes #5.