Harden rm -rf against empty or root TARGET (ShellCheck)

[NathanNeurotic]

Motivation

• Fix a critical ShellCheck/Codacy finding about unsafe rm -rf usage in mk_kelf.sh.
• Ensure rm -rf never operates on root (/) or an empty/unset TARGET value.
• Fail fast when TARGET is unset or empty using the required ${TARGET:?} pattern.
• Preserve existing behavior for valid TARGET paths during cleanup.

Description

• Add a POSIX validation line : "${TARGET:?TARGET is not set or empty}" immediately before removal.
• Add an explicit guard that errors and exits if TARGET equals / using if [ "$TARGET" = "/" ]; then ... fi.
• Use rm -rf -- "${TARGET:?}/" so ${TARGET:?} is used directly in the removal command to satisfy ShellCheck.
• Update only mk_kelf.sh (resulting in 7 insertions and 6 deletions).

Testing

• No automated tests were executed after this change.

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Codex Task

[codacy-production]

Codacy's Analysis Summary

0 new issue (≤ 0 issue)
0 new security issue

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