Add Blackbox AI to agents list (#365)

Author: ignatov

docs/overview/agents.mdx

@@ -7,6 +7,7 @@ The following agents can be used with an ACP Client:
 
 - [AgentPool](https://phil65.github.io/agentpool/advanced/acp-integration/)
 - [Augment Code](https://docs.augmentcode.com/cli/acp)
+- [Blackbox AI](https://docs.blackbox.ai/features/blackbox-cli/introduction)
 - [Claude Code](https://docs.anthropic.com/en/docs/claude-code/overview) (via [Zed's SDK adapter](https://github.com/zed-industries/claude-code-acp))
 - [Codex CLI](https://developers.openai.com/codex/cli) (via [Zed's adapter](https://github.com/zed-industries/codex-acp))
 - [Code Assistant](https://github.com/stippi/code-assistant?tab=readme-ov-file#configuration)