refactor: replace fetch_instructions with skill tool and built-in skills #22245

Job	Run time
knip	54s
check-translations	37s
compile	2m 35s
check-openrouter-api-key	3s
platform-unit-test (windows-latest)	5m 54s
platform-unit-test (ubuntu-latest)	5m 44s
integration-test	3m 39s
	19m 26s

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