PR #114 pointed @lead/@ops at xai/grok-4.5 but never gave opencode a
provider config for it — xai is not a built-in like anthropic was, it
needs the same explicit OpenAI-compatible block as ollama/ollama-cloud
(confirmed by the prior, never-merged investigation in PR #110). Without
this, any @lead/@ops run fails immediately on an unresolvable provider.
Adds the xai provider block (baseURL https://api.x.ai/v1, models derived
from agents.json) and passes XAI_API_KEY into the Install-opencode step
(it was already added to the Run-agent step in #114).
Felix Faerber