docs(skills): add build style skill

src/skills/style/build/SKILL.md

@@ -0,0 +1,9 @@
+---
+name: build-style
+description: Use when creating, editing, or reviewing Bazel `BUILD` files or Rust `Cargo.toml` package manifests in this repository.
+---
+
+# build-style
+
+Use this skill for Bazel `BUILD` files and Rust `Cargo.toml` package manifests.
+Follow the shared style skill instructions in `src/skills/style/STYLE.md`.