fix: wire MCP gateway into Gemini CLI settings

The MCP gateway writes github and safeoutputs server config to
.gemini/settings.json, but uses host.docker.internal URLs which
don't resolve on the host runner (only inside Docker containers).

Gemini runs directly on the host (unlike Claude which runs inside
AWF), so the URLs need to use localhost instead.

This patch:
- Replaces host.docker.internal with localhost in settings.json
- Sets trust=true on MCP servers for --yolo mode compatibility
- Logs the final settings for debugging

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

Author: lpcox