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/cli.py

@@ -140,6 +140,11 @@ def create_parser() -> argparse.ArgumentParser:
             "the host is built with Cargo."
         ),
     )
+    parser.add_argument(
+        "--exec-server-bin",
+        type=Path,
+        help="Optional prebuilt codex-exec-server executable. If omitted, build it with Cargo.",
+    )
     parser.add_argument(
         "--bwrap-bin",
         type=Path,
@@ -210,6 +215,11 @@ def assemble_package(args: argparse.Namespace) -> Path:
             "prebuilt code-mode host executable",
             "--code-mode-host-bin",
         ),
+        exec_server_bin=resolve_optional_input_path(
+            args.exec_server_bin,
+            "prebuilt executor executable",
+            "--exec-server-bin",
+        ),
         bwrap_bin=resolve_optional_input_path(
             args.bwrap_bin,
             "prebuilt Linux bwrap executable",
@@ -229,6 +239,7 @@ def assemble_package(args: argparse.Namespace) -> Path:
     inputs = PackageInputs(
         entrypoint_bin=source_outputs.entrypoint_bin,
         code_mode_host_bin=source_outputs.code_mode_host_bin,
+        exec_server_bin=source_outputs.exec_server_bin,
         rg_bin=resolve_rg_bin(spec, args.rg_bin),
         bwrap_bin=source_outputs.bwrap_bin,
         codex_command_runner_bin=source_outputs.codex_command_runner_bin,
@@ -239,6 +250,7 @@ def assemble_package(args: argparse.Namespace) -> Path:
     for filename, prebuilt in (
         (variant.entrypoint_name(spec), args.entrypoint_bin),
         (f"codex-code-mode-host{spec.exe_suffix}", args.code_mode_host_bin),
+        (f"codex-exec-server{spec.exe_suffix}", args.exec_server_bin),
     ):
         if args.strip == "all" or (
             args.strip == "auto"