Support a configurable Command Code home directory.

Feature Description

Command Code currently stores user-level data in ~/.commandcode with no way to change the base directory.

Add a COMMANDCODE_HOME environment variable, defaulting to ~/.commandcode, and resolve all user-level paths relative to it.

Example:

COMMANDCODE_HOME="${XDG_CONFIG_HOME}/commandcode" cmd

Use Case

Users following the XDG Base Directory Specification, using encrypted or separate storage, or managing multiple environments need control over where Command Code stores its data.

This also avoids placing application-specific directories directly under $HOME.

Additional Context

Other coding agents already provide this:

• Codex: CODEX_HOME
• Claude Code: CLAUDE_CONFIG_DIR
• pi: PI_CODING_AGENT_DIR

The default ~/.commandcode location should remain unchanged for backwards compatibility. Project-local .commandcode directories should continue working as they do currently.

How important is this to you?

Blocking adoption or production use

首先定位解析 ~/.commandcode 当前用户级路径和 cmd 入口点的代码。确认 COMMANDCODE_HOME 会覆盖默认值，所有用户级路径都使用它，默认值保持不变，并且项目本地的 .commandcode 目录继续正常工作。