brush: vendor the source tree (un-ignore) to complete the local fork

The prior commit switched the recipe to `[source] path = "source"`, but
.gitignore:77 still listed `local/recipes/shells/brush/source` (a leftover from
when brush was a transient upstream git fetch), so the vendored tree was not
tracked — a fresh clone would have no brush source and the build would fail.
Drop that ignore line and commit the vendored working tree (reubeno/brush @
897b373e, with the Redox port patches pre-applied). brush is now a durable
local fork like the other path=source recipes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

local/recipes/shells/brush/source/scripts/test-code-coverage.sh

@@ -0,0 +1,16 @@
+#!/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}"
+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/.*"