Ship codex-exec-server in CLI and app-server packages (#57590)

## What changed

- Build and bundle the standalone executor in `bin/` for both package variants, and advertise its path through `execServer` in `codex-package.json`.
- Include the executor in Cargo and Bazel release packaging, macOS signing and notarization, and Windows signing verification. Preserve prebuilt signed binaries during packaging.
- Make installers detect a missing advertised executor while continuing to accept older packages without it.

## Testing

Add coverage for executor archive contents and executable permissions, signed binary preservation, and macOS entitlement verification. Add package smoke tests for initialization, version reporting, filesystem and process sandbox enforcement, and startup error parity with `codex exec-server`.

GitOrigin-RevId: 5c0027fc19f16cf9c2a5bb52dbd065a9776bc2af

scripts/codex_package/layout.py

@@ -55,6 +55,11 @@ def build_package_dir(
         bin_dir / f"codex-code-mode-host{spec.exe_suffix}",
         is_windows=spec.is_windows,
     )
+    copy_executable(
+        inputs.exec_server_bin,
+        bin_dir / f"codex-exec-server{spec.exe_suffix}",
+        is_windows=spec.is_windows,
+    )
     copy_executable(inputs.rg_bin, path_dir / spec.rg_name, is_windows=spec.is_windows)
 
     if inputs.bwrap_bin is not None:
@@ -80,6 +85,7 @@ def build_package_dir(
         "target": spec.target,
         "variant": variant.name,
         "entrypoint": f"bin/{entrypoint_name}",
+        "execServer": f"bin/codex-exec-server{spec.exe_suffix}",
         "resourcesDir": "codex-resources",
         "pathDir": "codex-path",
     }
@@ -113,6 +119,7 @@ def validate_package_dir(
         "target": spec.target,
         "variant": variant.name,
         "entrypoint": f"bin/{variant.entrypoint_name(spec)}",
+        "execServer": f"bin/codex-exec-server{spec.exe_suffix}",
         "resourcesDir": "codex-resources",
         "pathDir": "codex-path",
     }
@@ -126,6 +133,7 @@ def validate_package_dir(
     required_files = [
         Path("bin") / variant.entrypoint_name(spec),
         Path("bin") / f"codex-code-mode-host{spec.exe_suffix}",
+        Path("bin") / f"codex-exec-server{spec.exe_suffix}",
         Path("codex-path") / spec.rg_name,
     ]
     executable_files = list(required_files)