scripts: refactor and review

[noahehall]

moving pretty fast and not following best practices

• ensure atleast set -eu at top
• no hardcoded values, vars et at top
• no logic embedded in case structs; call functions at top
• no multi level if statements: use case structs
• no hella long if else if, else if, else ifs, use case statements
• ensure help is provided if invalid input received
• add DEBUG=${NIRV_SCRIPT_DEBUG:-''} to all scripts to enable debugging via 1 env var (see script.vault.sh)
• update nirvai/docs/scripts readme.md
  • ensure interfaces are clearly stated
  • ensure all copypasta works
  • ensure basic workflow provided
• no bash, keep it posix compliant (there might be a ticket for this already)
• decompose into multiple files, e.g. they should all share the same base interface