CLI fails to start after brew upgrade removes the pinned Homebrew Node keg #446

Description

After running brew upgrade on macOS with a Homebrew-managed Node.js, the MiniMax Code CLI fails to start with an error like:

sh: /opt/homebrew/Cellar/node/26.7.0/bin/node: not found   (exit 127)

Reproduction

1. macOS with Node installed via Homebrew (/opt/homebrew/bin/node resolving into Cellar/node/<version>/bin/node).
2. Install MiniMax Code with the official install script (curl installer) while that Node version is active. The install receipt (~/.minimax-code/install.json) and the versioned launchers record the resolved Cellar path.
3. Run brew upgrade (or brew upgrade node), which removes the old versioned Cellar keg.
4. Run mcode. The launcher execs the removed Cellar path and fails with "not found"; there is no self-healing path from inside the CLI.

Expected behavior

• Launchers keep working across Homebrew Node upgrades, for example by pinning the formula-managed stable path (<brew>/opt/node/bin/node) instead of the versioned keg.
• In-app updates migrate existing receipts that already recorded a Cellar path, so installs heal on their next update.
• When the pinned Node is missing, the launcher prints a repair hint pointing at rerunning the installer.

Environment

• macOS (Homebrew on /opt/homebrew; Intel Homebrew and Linuxbrew layouts are equally affected)
• Node installed via Homebrew
• MiniMax Code installed via the official install script

Fix in progress: #445 (TUI update side: receipt migration to the opt path, repair hint, startup diagnostics). Installer-side recording of the stable path ships with the installer release process.