chore(mcp): OpenAI plugin domain-verification token for mcp.zernio.com

The portal issued this token for the Zernio plugin draft; it is public
proof of control, not a secret, so it ships as the default and stays
overridable through the environment.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: mikipalet

src/late/mcp/constants.py

@@ -35,7 +35,7 @@
 # OpenAI plugin domain verification: the portal issues one token per plugin
 # and expects it as the bare body of this path on the MCP host.
 ENDPOINT_OPENAI_APPS_CHALLENGE = "/.well-known/openai-apps-challenge"
-OPENAI_APPS_CHALLENGE_TOKEN = os.getenv("OPENAI_APPS_CHALLENGE_TOKEN", "")
+OPENAI_APPS_CHALLENGE_TOKEN = os.getenv("OPENAI_APPS_CHALLENGE_TOKEN", "j_VHjxLGc6YGRVi1l8-L48C1espKIwoA9jCbPopWUH4")
 
 # --- OAuth 2.0 protected-resource discovery (RFC 9728 / MCP authorization spec) ---
 # This MCP server is a *resource server*: it does not mint tokens, it accepts