[codex] Switch default chat to TUI v2

[roackb2]

Summary

• route bare heddle and heddle chat to the API-backed TUI v2 command path
• add heddle chat-v1 plus dev script variants as the explicit legacy TUI escape hatch
• update focused docs and routing coverage for the default-chat cutover

Expected behavior change

• normal interactive chat now starts TUI v2 and can attach/embed the shared control-plane server
• legacy TUI remains available through chat-v1 and chat:dev:v1
• non-chat commands are unchanged

Verification

• yarn -s vitest run src/__tests__/unit/cli/main-command-routing.test.ts
• yarn typecheck
• yarn lint
• yarn test:unit
• yarn -s cli:dev --help

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid attaching default chat to another embedded TUI

When heddle chat now delegates to runChatCliV2Command, it inherits resolveChatV2Runtime's attach-to-any-fresh-server behavior, including a live server whose registry mode is embedded-chat. In that scenario the backend is owned by another terminal chat and runtime.close is a no-op for this client, so if the original TUI exits this default chat loses its control-plane server and subsequent requests fail; attaching is safe for daemon mode, but default chat should start its own embedded server or only attach to daemon-owned servers.

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