fix: detect missing terminal compilers before interactive runs

[jerewy]

Summary

• add terminal marker watchers to detect command availability and hide probe markers from the displayed terminal output
• verify C/C++/Java toolchains before launching interactive runs and fall back to the standard executor when the sandbox lacks the runtime
• surface clearer interactive fallback toasts when the terminal is ready but missing required compilers

Testing

• npm run lint (fails: ESLint must be installed: npm install --save-dev eslint)

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https://chatgpt.com/codex/tasks/task_e_68da3eb097b0833280f3444d64caa08b