fix: various fixes

[xphir]

Purpose

This pull request improves shell script configurations, fixes file references, and enhances code readability:

• Enabled external-sources in .shellcheckrc to follow external file references.
• Corrected shellcheck file paths for shared.bash and steps.bash in command.
• Fixed a typo ("fragements" → "fragments") and simplified metadata retrieval logic in command.
• Added a shellcheck directive in steps.bash to handle dynamic sourcing of environment files.

[madobrien]

Thanks for the fixups!