fix: integration test for #9011 (#9166)

Adds an integration test for the new behavior introduced in
https://github.com/openai/codex/pull/9011. The work to create the test
setup was substantial enough that I thought it merited a separate PR.

This integration test spawns `codex` in TUI mode, which requires
spawning a PTY to run successfully, so I had to introduce quite a bit of
scaffolding in `run_codex_cli()`. I was surprised to discover that we
have not done this in our codebase before, so perhaps this should get
moved to a common location so it can be reused.

The test itself verifies that a malformed `rules` in `$CODEX_HOME`
prints a human-readable error message and exits nonzero.

codex-rs/Cargo.lock

@@ -1746,6 +1746,7 @@ dependencies = [
  "codex-app-server-protocol",
  "codex-arg0",
  "codex-backend-client",
+ "codex-cli",
  "codex-common",
  "codex-core",
  "codex-feedback",
@@ -1753,6 +1754,8 @@ dependencies = [
  "codex-login",
  "codex-protocol",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
+ "codex-utils-pty",
  "codex-windows-sandbox",
  "color-eyre",
  "crossterm",
@@ -1818,6 +1821,7 @@ dependencies = [
  "codex-app-server-protocol",
  "codex-arg0",
  "codex-backend-client",
+ "codex-cli",
  "codex-common",
  "codex-core",
  "codex-feedback",
@@ -1826,6 +1830,8 @@ dependencies = [
  "codex-protocol",
  "codex-tui",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
+ "codex-utils-pty",
  "codex-windows-sandbox",
  "color-eyre",
  "crossterm",