Mirrors the existing nextcloud-claude-bot setup but invokes `opencode run`
against the local `halo-8000` provider/model. The bot listens on
127.0.0.1:8086, is exposed via the `/_opencode-bot/` location on
nc.hoyer.xyz, and uses `@Halo` as its mention trigger in group chats.
The opencode config (config/opencode/config.json) is installed into the
service's $HOME/.config/opencode/ on each start, so the bot picks up the
same provider definition the user uses interactively. The model map keys
are renamed to `halo-8000` / `halo-8001` so the canonical
`provider/model` reference works without an alias indirection.
