feat: enhance gum installation check for cross-platform compatibility

[ronibhakta1]

This pull request improves the require_gum() function in scripts/configure.sh to better support different operating systems and architectures when downloading the gum binary. The changes also update the error messaging for failed installations.

Cross-platform and architecture support:

• The OS detection logic now explicitly supports both Darwin (macOS) and Linux, and only attempts to auto-download gum on these platforms. Other platforms will prompt the user to install manually.
• Architecture detection has been improved to treat both arm64 and aarch64 as arm64, ensuring correct binary selection for multiple ARM variants.
• The download URL for the gum binary now dynamically uses the detected OS and architecture, making the script compatible with both macOS and Linux.

Error handling and messaging:

• The error message for failed auto-downloads has been updated to only reference the upstream installation instructions, removing the brew-specific suggestion to avoid confusion on non-macOS systems.