build: unify production crates and vendor the patched shell

Assisted-by: SurmAgent:OpenAI

userland/brush/source/scripts/test-code-coverage.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/bash
+set -euo pipefail
+
+script_dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)
+workspace_root="$(realpath "${script_dir}/..")"
+
+export CARGO_TARGET_DIR="${workspace_root}/target/cov"
+
+cd "${workspace_root}"
+# shellcheck source=/dev/null
+source <(cargo llvm-cov show-env --export-prefix)
+
+cargo llvm-cov clean --workspace
+
+cargo test -- --show-output || true
+
+cargo llvm-cov report --html --ignore-filename-regex "target/.*"