fix: checkout uscope into workspace and symlink for CI path dep

actions/checkout@v4 requires paths under the workspace directory.
Checkout uscope-checkout inside the workspace, then symlink it to
../uscope where Cargo.toml expects it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ci: add release workflow for macOS ARM and Linux

Triggers on version tags (v*), builds release binaries for both
platforms, and publishes them as GitHub Release assets.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>