[codex] Fix Windows BuildBuddy Bazel wrapper execution (#25915)

## Why

#25156 moved Bazel CI launches into a shared Python wrapper. On Windows,
launching Bazel with `os.execvp` can split the spaced
`--test_env=PATH=...` argument and fail to propagate the eventual Bazel
exit status, allowing jobs to pass without running tests. This reapplies
the wrapper after #25909 with a Windows-safe launch path.

## What changed

Use a waited `subprocess.run` launch on Windows while preserving
`os.execvp` on Unix. Add a process-level regression test for spaced
arguments and child exit status, and run it on Windows Bazel shard 1.

## Experiment

To confirm Bazel was actually invoking tests, patch `87b61d0be6`
temporarily added an intentionally failing `codex-core` unit test. Bazel
failed on that sentinel on all three major platforms:

- [Linux Bazel
test](https://github.com/openai/codex/actions/runs/26841132773/job/79151062486)
- [macOS Bazel
test](https://github.com/openai/codex/actions/runs/26841132773/job/79151062362)
- [Windows Bazel test shard
1/4](https://github.com/openai/codex/actions/runs/26841132773/job/79151062155)

The sentinel was removed after collecting this evidence. Windows Bazel
[clippy](https://github.com/openai/codex/actions/runs/26841132773/job/79151062914)
and [release
verification](https://github.com/openai/codex/actions/runs/26841132773/job/79151062739)
also passed.

## Validation

After removing the sentinel, `just test -p codex-core` no longer
reported it. The local run retained two unrelated environment-specific
failures.

justfile

@@ -83,6 +83,12 @@ test *args:
     $env:RUST_MIN_STACK = "{{ rust_min_stack }}"; cargo nextest run --no-fail-fast @($args | Select-Object -Skip 1)
     just bench-smoke
 
+# Run from the repository root so scripts that resolve paths from `cwd` see
+# the same layout they use in GitHub Actions.
+[no-cd]
+test-github-scripts:
+    {{ python }} -m unittest discover -s {{ justfile_directory() }}/.github/scripts -p 'test_*.py'
+
 # Run explicit workspace benchmark targets.
 bench *args:
     cargo bench --workspace --bench '*' {args}
@@ -129,11 +135,8 @@ bazel-clippy:
 bazel-argument-comment-lint:
     bazel build --config=argument-comment-lint -- $({{ justfile_directory() }}/tools/argument-comment-lint/list-bazel-targets.sh)
 
-bazel-remote-test:
-    bazel test --test_tag_filters=-argument-comment-lint //... --config=remote --platforms=//:rbe --keep_going
-
 build-for-release:
-    bazel build //codex-rs/cli:release_binaries --config=remote
+    bazel build //codex-rs/cli:release_binaries
 
 # Run the MCP server
 mcp-server-run *args: