Restrict accessibility bridge to Windows/macOS and add Linux GPU detection in doctor

[AmrDab]

Motivation

• Prevent the accessibility bridge from attempting platform scripts on unsupported platforms (e.g. Linux) and provide clearer error messages.
• Improve hardware reporting by adding GPU detection for Linux systems so the doctor can report GPU names and VRAM where available.

Description

• Added a SUPPORTED_PLATFORMS set for win32 and darwin and early-return logging in isShellAvailable() when the current platform is not supported.
• Added an early rejection in runScript() for unsupported platforms and removed the fallback mapping to Windows scripts so only the platform's script map is used.
• Added Linux GPU detection in detectGpuInfo() which prefers nvidia-smi output and falls back to parsing lspci for VGA/3D devices, returning formatted GPU names and memory when available.
• Kept existing timeouts and error messaging for macOS/Windows shell probes and script execution behavior unchanged.

Testing

• Ran TypeScript type-check with tsc --noEmit which completed successfully.
• Executed the repository test suite with npm test and the automated tests passed.
• Built and ran the CLI doctor flow on a macOS test machine to confirm no regressions in accessibility probing and on a Linux container to validate the new GPU detection path (both succeeded).

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Codex Task