chore(frontend): upgrade Angular 19 -> 21 #136

Job	Run time
version	7s
frontend	56s
backend (linux-amd64, ubuntu-latest)	1m 10s
backend (linux-arm64, ubuntu-24.04-arm)	1m 7s
backend-multi-arch	21s
full (linux-arm64, ubuntu-24.04-arm)	33s
full (linux-amd64, ubuntu-latest)	35s
full-multi-arch	25s
helm	11s
	5m 25s

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