Add a conservative source-checkout setup helper based on the Linux quick-start intent from PR #54.
The script builds the CLI/recompiler tools, refreshes BIOS C when a BIOS is present, and builds the BIOS-only runtime only when BIOS/generated sources are available. It deliberately leaves game project creation to the existing CLI generator.
Co-authored-by: Keeganator <keegan.pan@gmail.com>