feat: initial checkpoint as state-driven UI element #22256

Job	Run time
check-translations	31s
knip	1m 3s
check-openrouter-api-key	3s
compile	2m 34s
platform-unit-test (windows-latest)	11m 40s
platform-unit-test (ubuntu-latest)	6m 23s
integration-test	3m 26s
	25m 40s

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