fix: keep zsh-fork release assets after removing shell-tool-mcp (#15644)

## Why

`shell-tool-mcp` and the Bash fork are no longer needed, but the patched
zsh fork is still relevant for shell escalation and for the
DotSlash-backed zsh-fork integration tests.

Deleting the old `shell-tool-mcp` workflow also deleted the only
pipeline that rebuilt those patched zsh binaries. This keeps the package
removal, while preserving a small release path that can be reused
whenever `codex-rs/shell-escalation/patches/zsh-exec-wrapper.patch`
changes.

## What changed

- removed the `shell-tool-mcp` workspace package, its npm
packaging/release jobs, the Bash test fixture, and the remaining
Bash-specific compatibility wiring
- deleted the old `.github/workflows/shell-tool-mcp.yml` and
`.github/workflows/shell-tool-mcp-ci.yml` workflows now that their
responsibilities have been replaced or removed
- kept the zsh patch under
`codex-rs/shell-escalation/patches/zsh-exec-wrapper.patch` and updated
the `codex-rs/shell-escalation` docs/code to describe the zsh-based flow
directly
- added `.github/workflows/rust-release-zsh.yml` to build only the three
zsh binaries that `codex-rs/app-server/tests/suite/zsh` needs today:
  - `aarch64-apple-darwin` on `macos-15`
  - `x86_64-unknown-linux-musl` on `ubuntu-24.04`
  - `aarch64-unknown-linux-musl` on `ubuntu-24.04`
- extracted the shared zsh build/smoke-test/stage logic into
`.github/scripts/build-zsh-release-artifact.sh`, made that helper
directly executable, and now invoke it directly from the workflow so the
Linux and macOS jobs only keep the OS-specific setup in YAML
- wired those standalone `codex-zsh-*.tar.gz` assets into
`rust-release.yml` and added `.github/dotslash-zsh-config.json` so
releases also publish a `codex-zsh` DotSlash file
- updated the checked-in `codex-rs/app-server/tests/suite/zsh` fixture
comments to explain that new releases come from the standalone zsh
assets, while the checked-in fixture remains pinned to the latest
historical release until a newer zsh artifact is published
- tightened a couple of follow-on cleanups in
`codex-rs/shell-escalation`: the `ExecParams::command` comment now
describes the shell `-c`/`-lc` string more clearly, and the README now
points at the same `git.code.sf.net` zsh source URL that the workflow
uses

## Testing

- `cargo test -p codex-shell-escalation`
- `just argument-comment-lint`
- `bash -n .github/scripts/build-zsh-release-artifact.sh`
- attempted `cargo test -p codex-core`; unrelated existing failures
remain, but the touched `tools::runtimes::shell::unix_escalation::*`
coverage passed during that run

.github/workflows/rust-release.yml

@@ -389,15 +389,6 @@ jobs:
       release-lto: ${{ contains(github.ref_name, '-alpha') && 'thin' || 'fat' }}
     secrets: inherit
 
-  shell-tool-mcp:
-    name: shell-tool-mcp
-    needs: tag-check
-    uses: ./.github/workflows/shell-tool-mcp.yml
-    with:
-      release-tag: ${{ github.ref_name }}
-      publish: true
-    secrets: inherit
-
   argument-comment-lint-release-assets:
     name: argument-comment-lint release assets
     needs: tag-check
@@ -405,12 +396,17 @@ jobs:
     with:
       publish: true
 
+  zsh-release-assets:
+    name: zsh release assets
+    needs: tag-check
+    uses: ./.github/workflows/rust-release-zsh.yml
+
   release:
     needs:
       - build
       - build-windows
-      - shell-tool-mcp
       - argument-comment-lint-release-assets
+      - zsh-release-assets
     name: release
     runs-on: ubuntu-latest
     permissions:
@@ -453,11 +449,8 @@ jobs:
       - name: List
         run: ls -R dist/
 
-      # This is a temporary fix: we should modify shell-tool-mcp.yml so these
-      # files do not end up in dist/ in the first place.
       - name: Delete entries from dist/ that should not go in the release
         run: |
-          rm -rf dist/shell-tool-mcp*
           rm -rf dist/windows-binaries*
           # cargo-timing.html appears under multiple target-specific directories.
           # If included in files: dist/**, release upload races on duplicate
@@ -547,6 +540,13 @@ jobs:
           tag: ${{ github.ref_name }}
           config: .github/dotslash-config.json
 
+      - uses: facebook/dotslash-publish-release@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag: ${{ github.ref_name }}
+          config: .github/dotslash-zsh-config.json
+
       - uses: facebook/dotslash-publish-release@v2
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}