feat(shell-tool-mcp): add patched zsh build pipeline (#11668)

## Summary
- add `shell-tool-mcp/patches/zsh-exec-wrapper.patch` against upstream
zsh `77045ef899e53b9598bebc5a41db93a548a40ca6`
- add `zsh-linux` and `zsh-darwin` jobs to
`.github/workflows/shell-tool-mcp.yml`
- stage zsh binaries under `artifacts/vendor/<target>/zsh/<variant>/zsh`
- include zsh artifact jobs in `package.needs`
- mark staged zsh binaries executable during packaging

## Notes
- zsh source is cloned from `https://git.code.sf.net/p/zsh/code`
- workflow pins zsh commit `77045ef899e53b9598bebc5a41db93a548a40ca6`
- zsh build runs `./Util/preconfig` before `./configure`

## Validation
- parsed workflow YAML locally (`yaml-ok`)
- validated zsh patch applies cleanly with `git apply --check` on a
fresh zsh clone

shell-tool-mcp/patches/bash-exec-wrapper.patch

@@ -6,7 +6,7 @@ index 070f5119..d20ad2b9 100644
    char sample[HASH_BANG_BUFSIZ];
    size_t larray;
  
-+  char* exec_wrapper = getenv("BASH_EXEC_WRAPPER");
++  char* exec_wrapper = getenv("EXEC_WRAPPER");
 +  if (exec_wrapper && *exec_wrapper && !whitespace (*exec_wrapper))
 +    {
 +      char *orig_command = command;