1. 1. Summary

• Fix `bazel run //:format` failing on macOS (and other unsupported platforms) due to the noop toolchain
• Add `package(default_visibility = ["//visibility:public"])` to the noop toolchain BUILD file so `//:clang_format` alias can resolve
• Replace the empty `clang_format` filegroup with an `sh_binary` wrapping a no-op stub script, so `format_multirun` doesn't fail with "expands to no files"

1. 1. Test plan

• [x] Verified `bazel run //:format` completes successfully on macOS (previously failed with visibility and "expands to no files" errors)
• [ ] Verify Linux CI still passes (real toolchain has its own BUILD template with `package(default_visibility)` already set)

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