docs(skills): add build style skill

src/skills/style/build/rules/dependencies.md

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+# Dependency rules
+
+## Use workspace dependency versions
+
+### Rule
+
+Declare Rust dependency versions in the repository root `Cargo.toml` under `[workspace.dependencies]`.
+Reference workspace dependencies from package `Cargo.toml` files with `workspace = true`.
+Do not declare dependency versions in package `Cargo.toml` files unless the operator explicitly requests a package-local version.
+Add package-local dependency features only when the feature set is specific to that package.
+
+### Rationale
+
+The repository has one Cargo workspace and one `Cargo.lock`.
+Centralized versions keep package manifests consistent with the workspace lockfile.
+
+## Declare Rust dependencies in each build system
+
+### Rule
+
+Declare each direct crate dependency in each build system that builds the Rust target.
+For Cargo, declare the crate in the package `Cargo.toml` file.
+Use `workspace = true` for workspace-managed dependencies.
+For Bazel, add the crate label to the `deps` of the target that uses it.
+Apply this rule to `rust_library`, `rust_binary`, and `rust_test` targets.
+
+### Rationale
+
+Cargo and Bazel resolve Rust dependencies independently.
+Complete declarations keep Cargo, Rust Analyzer, and Bazel builds consistent.