Add ZeroClick ad fallback (#642) #628

Job	Run time
build-freebuff	1m 15s
build-and-smoke-freebuff-windows	2m 38s
e2e-version	1m 11s
e2e-ads-behavior	1m 9s
e2e-slash-commands	53s
e2e-help-command	1m 27s
e2e-terminal-command	56s
e2e-code-edit	1m 13s
e2e-agent-startup	2m 5s
e2e-startup	1m 8s
	13m 55s

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