Adopt conventions from the official android/skills repo

Google published an official skills repo ([github.com/android/skills]()) for Android agent skills — no public contributions accepted, but review its structure/conventions and align our internal skills (btrace-perfetto, create-java-pr, etc.) where it makes sense.

Review the structure and conventions in the official android/skills repository first, then inspect the internal skills named in the issue, including btrace-perfetto and create-java-pr. Compare their organization and conventions, and document or implement only the alignments that make sense for this repository; done means the relevant internal skills follow an agreed convention.

索引モデルが issue の本文から書いたものです。