[codex] Revert shared BuildBuddy Bazel wrapper (#25909)

## Why

PR #25905 intentionally adds a failing `codex-core` unit test, but its
[Bazel test on Windows
check](https://github.com/openai/codex/actions/runs/26837526950/job/79135369259)
passed. That shows the Bazel configuration introduced by #25156 is not
behaving as expected, so revert it while the configuration can be
investigated separately.

## What changed

Revert #25156 in full, restoring the previous Bazel remote
configuration, CI scripts, workflows, `rusty_v8` handling, and
documentation. This removes the shared BuildBuddy wrapper and its tests.

## Validation

Not run locally; this exact revert was prioritized for a fast rollback.

justfile

@@ -83,12 +83,6 @@ 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}
@@ -135,8 +129,11 @@ 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
+    bazel build //codex-rs/cli:release_binaries --config=remote
 
 # Run the MCP server
 mcp-server-run *args: