Add GitHub Actions workflow for multi-platform builds

[beNative]

Summary

• add a GitHub Actions workflow that runs on Ubuntu, macOS, and Windows
• build Electron packages and upload the generated release artifacts for each platform

Testing

• not run (workflow change)

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https://chatgpt.com/codex/tasks/task_e_68f25ab9be688332a8e7de54e11d85e2

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Disable macOS code signing in CI build

The workflow invokes npm run pack on macOS runners without disabling code signing. electron-builder enables signing by default on mac builds and fails when no signing identity is available, which is the case on GitHub-hosted macOS runners. As written, the macOS job will error with “No identity found for signing” instead of uploading artifacts. Consider setting CSC_IDENTITY_AUTO_DISCOVERY: false (or mac.identity: null in config) for CI builds so the packaging step can complete unsigned.

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