Sign bundled macOS helper binaries (#35264)

## Why

The macOS release workflow fetched `rg` and zsh while assembling package
archives, after the signing stage. This left the bundled helper executables
outside the workflow's signing and notarization checks.

## What changed

- Fetch, sign, notarize, and upload the pinned macOS `rg` and zsh binaries with
  the other release artifacts.
- Build package archives from those signed helpers via `--rg-bin` and the new
  `--zsh-bin` override.
- Verify the helpers' architecture, signatures, and absence of entitlements in
  the final package.

## Testing

- Cover the prebuilt zsh override and verify that package assembly preserves
  the supplied helper binaries.

GitOrigin-RevId: a3865c04fa2f0f4df32e627ee7202bc87bdc3241

scripts/codex_package/zsh.py

@@ -5,6 +5,7 @@ from pathlib import Path
 from .dotslash import fetch_dotslash_executable
 from .targets import REPO_ROOT
 from .targets import TargetSpec
+from .targets import resolve_input_path
 
 
 ZSH_MANIFEST = REPO_ROOT / "scripts" / "codex_package" / "codex-zsh"
@@ -14,7 +15,12 @@ ZSH_RESOURCE_PATH = Path("zsh") / "bin" / "zsh"
 def resolve_zsh_bin(
     spec: TargetSpec,
     manifest_path: Path | None = None,
+    *,
+    zsh_bin: Path | None = None,
 ) -> Path | None:
+    if zsh_bin is not None:
+        return resolve_input_path(zsh_bin, "zsh executable", "--zsh-bin")
+
     return fetch_dotslash_executable(
         spec,
         manifest_path=manifest_path or ZSH_MANIFEST,