fix: add MCP gateway connection to OpenCode config

OpenCode was not connecting to the MCP gateway for safe-output tools.
The agent ran successfully (LLM calls worked) but never called
add_comment because it had no MCP server configured.

Add 'mcp.safeoutputs' config to opencode.jsonc pointing to the
MCP gateway at host.docker.internal:<port> with proper auth header.
This matches how Codex connects to the gateway via HTTP MCP.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lpcox