Codex CLI 0.139.0

• [changed] Release channel updated from alpha to stable.

Under the hood

• Removed the git-utils/src/fsmonitor.rs and tui/src/thread_transcript.rs modules along with their associated source subsystems.
• Dropped the AgentMessageInvocationArgs and SubAgentActivityEvent data models and the ThreadItem::SubAgentActivity variant.
• Cleaned up several related enum variants in approval actions, login parameters, sandbox policy deserialization, server requests, and thread items.