refactor: Rename sandbox to runtime and fix terminal hook

[Che-Zhu]

Description

This PR performs two main cleanup tasks:

1. Renames the sandbox directory to runtime.
2. Refactors useTerminal hook to fix React warning.

Changes

• Renamed sandbox/ to runtime/.
• Updated workflow and README.
• Refactored useTerminal to avoid synchronous setState in useEffect.

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  Commit: 6f6c20b3aa5a885bf6f74e842f6de2ea0aff7171
  Branch: refactor/rename-sandbox-to-runtime-and-fix-terminal

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