Add completion spec: Codex (codex)

Add command completion spec for OpenAI's Codex CLI, covering:
- Global options (--model, --sandbox, --config, --image, etc.)
- Subcommands: exec, login, logout, completion, resume, fork,
  apply, cloud, features, mcp, mcp-server, app, app-server,
  execpolicy, sandbox, debug
- Nested subcommands (exec resume, cloud exec, features
  enable/disable/list, mcp add/remove/list/authenticate,
  sandbox macos/linux, debug app-server send-message-v2)
- Static suggestions for enum-like arguments (sandbox policies,
  approval modes, shell names, color modes)
- File/folder templates for path arguments

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: oz-agent