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

先定位解析 ~/.commandcode 目前使用者層級路徑和 cmd 進入點的程式碼。確認 COMMANDCODE_HOME 會覆寫預設值、所有使用者層級路徑都使用它、預設值維持不變，以及專案本機的 .commandcode 目錄仍能繼續運作。