Add failing tests for IMPORTANT audit findings (wave 5)

[kelp]

Summary

• Add failing integration tests for 6 IMPORTANT audit findings across mkdir, rmdir, mktemp, mv, and touch
• Tests encode correct GNU coreutils behavior; they fail against current code (TDD red phase)
• No implementation code modified

Findings Tested

Utility	Finding	Expected (GNU)	Actual (vibeutils)
mkdir	-m symbolic modes	Accepts u=rwx,go=rx	Rejects with "invalid mode"
mkdir	-p -m scope	Mode applies to leaf only	Mode applies to all intermediates
rmdir	-v --ignore-fail-on-non-empty	Still prints verbose	Verbose suppressed
mktemp	Implicit suffix	myapp.XXXXXXtxt succeeds	Rejected as "too few X's"
mv	Hardlink same-file	Exit 0, remove source	Exit 1 with error message
touch	-h implies -c	Does not create file	Creates regular file

Test plan

• All new tests verified to FAIL against current implementation
• No existing tests regressed
• Phase 2: fix implementations to make tests pass

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