feat(gateway): implement OpenResponses /v1/responses endpoint phase 2

- Add input_image and input_file support with SSRF protection
- Add client-side tools (Hosted Tools) support
- Add turn-based tool flow with function_call_output handling
- Export buildAgentPrompt for testing

src/commands/agent.ts

@@ -415,6 +415,7 @@ export async function agentCommand(
             skillsSnapshot,
             prompt: body,
             images: opts.images,
+            clientTools: opts.clientTools,
             provider: providerOverride,
             model: modelOverride,
             authProfileId,