refactor: delete dead-code duplicate src/types/config.ts (#3141)

* Initial plan

* refactor: remove dead duplicate src/types/config.ts and its test

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

src/types/config.test.ts

@@ -2,7 +2,7 @@
  * Docker and container configuration types for the agentic workflow firewall
  */
 
-import type { UpstreamProxyConfig } from './config';
+import type { UpstreamProxyConfig } from './upstream-proxy';
 
 /**
  * Configuration for the Squid proxy server