Fix multiple commands not working on Windows 11

[binary-blazer]

Related to #36

Fix errors in 'samurai bootstrap', 'samurai set brand stable', and 'samurai build' commands on Windows 11.

• src/commands/bootstrap.ts

  • Add a check for the existence of the mach command before executing it.
  • Provide a clear error message if the mach command is not found.

• src/commands/set.ts

  • Add a check for the existence of brandConfig before accessing its properties.
  • Provide a clear error message if brandConfig is undefined.

• src/commands/build.ts

  • Add a check for the existence of brandConfig before accessing its properties.
  • Provide a clear error message if brandConfig is undefined.

• docs/content/guides/windows.md

  • Add troubleshooting steps for common issues on Windows 11.
  • Include steps to check for the existence of the mach command.
  • Include steps to ensure samurai.json is correctly configured.