feat: 옵션 수정 불가능 사유를 좀 더 명시적으로 노출 #40

Job	Run time
config	2s
build (admin-dev, pyconkr-admin)	1m 6s
build (participant-dev, pyconkr-participant-portal)	46s
build (pyconkr-dev, pyconkr-2026)	41s
trigger	7s
	2m 42s

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