Add XAI Grok to the AI panel (#1558)

Grok Build is added as one more entry in the agent discovery list, over ACP, like the others. Thanks @cfaulkingham.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

docs/design/in-app-agent-chat.md

@@ -50,6 +50,7 @@ with SolidCraft, the user installs the agent.
 | Codex | `codex-acp` adapter (`@zed-industries/codex-acp` 0.16 moved to `@agentclientprotocol/codex-acp`) | `@agentclientprotocol/codex-acp` 2.2.2, Apache-2.0 | `--version` (0.16 rejected the flag; 2.x prints it) | Agent method `chat-gpt` (the adapter opens the browser for the ChatGPT login when the client calls `authenticate`), and `api-key` for a key the user configures in Codex. 0.16 also listed `env_var` methods for `CODEX_API_KEY` / `OPENAI_API_KEY`. The login is Codex's own: `~/.codex/auth.json`. |
 | Gemini CLI | built in: `gemini --acp` (the ACP registry's current flag; older releases used `--experimental-acp`) | `@google/gemini-cli` 0.64, Apache-2.0 | `--version` | Its own Google login (`~/.gemini/oauth_creds.json`) or a key in the environment. |
 | OpenCode | built in: `opencode acp` | `opencode-ai` 1.19, MIT | `--version` | Its own providers' logins (`~/.local/share/opencode/auth.json`) or keys in the environment. |
+| XAI Grok | built in: `grok agent stdio` | [Grok Build](https://github.com/xai-org/grok-build), Apache-2.0; installed separately | `grok --version` prints `grok 1.0.58 (…) [alpha]` (checked 2026-10-15; in-app connection also checked with 1.0.60) | Its own `~/.grok/auth.json` or `XAI_API_KEY`. `grok login` signs in in the browser; ACP advertises `cached_token` and `grok.com` authentication methods. |
 | Others in the ACP registry | `copilot --acp`, `qwen --acp`, `opencode acp`, `goose acp`, `cline --acp`, `kimi acp`, … | mixed; several are proprietary, one is GPL and one AGPL (we only start them as programs, never link them) | `--version` | each its own |
 
 The registry (`https://cdn.agentclientprotocol.com/registry/v1/latest/registry.json`) lists