Codex Plus runtime 0.1.0-preview.3

Adds native multi-environment selection keyed by canonical CODEX_HOME, with shared path precedence and a read-only codex-plus-context diagnostic.

Existing explicit state/config paths remain supported. No home migration, authentication copying or native daemon restart is performed. Notification relay/hook activation remains opt-in.

Source: c73c237

SHA-256: 43908c4b5b238fdbb81187050f0e7bfd4653a6f4d3677e1f1c9577ff443cd24f