Toolchain 0.6.0

Toolchain 0.6.0 improves Windows support and simplifies formatting, validation and SDK releases.

• Fix Windows tool resolution, Web execution and UTF-8 SDK packaging.
• Run host tests and benchmarks as standalone executables.
• Speed up formatting through parallel batches and shared structural analysis.
• Consolidate toolchain configuration and reuse cached compiler and SDK inputs.
• Run formatting, optimized host tests and packaging before creating the source snapshot from a clean Git commit.
• Reuse the configured Bazel server throughout SDK releases.

Upgrade notes

• Replace bazel build :sdk with bazel run :sdk. Remove separate snapshot() declarations.
• Use :tests_web and :benchmarks_web instead of running native targets with --config=web.
• Configure shared output-directory startup options in .bazelrc.

Windows runtime validation still requires a Windows host.