Use DeepSeek agent for BuffBench #576

Job	Run time
build-freebuff	1m 12s
build-and-smoke-freebuff-windows	2m 15s
e2e-version	1m 1s
e2e-agent-startup	2m 21s
e2e-ads-behavior	1m 11s
e2e-help-command	1m 23s
e2e-startup	1m 7s
e2e-code-edit	1m 6s
e2e-terminal-command	1m 2s
e2e-slash-commands	58s
	13m 36s

Provide feedback