chore: switch @lead/@ops from Anthropic to xAI grok-4.5

Removes the last Anthropic-model usage from the agent registry.
XAI_API_KEY was already provisioned as an org secret; wire it into
the run-agent step and update every doc/comment that referenced
ANTHROPIC_API_KEY or claude-opus-4-8.

.gitea/workflows/scripts/install-opencode.sh

@@ -42,7 +42,7 @@ PERM=$(jq -nc --argjson s "$SKILLS" '
 # The provider `models:` maps are DERIVED from agents.json (the single source of truth, shared with
 # route.sh) so every model an agent is routed to is always declared in the provider config.
 # `ollama-cloud/` prefix models go to the cloud provider; `ollama/` prefix models go to the local
-# provider. Built-in providers (e.g. `anthropic/claude-opus-4-8` for @lead) are not derived here.
+# provider. Built-in providers (e.g. `xai/grok-4.5` for @lead/@ops) are not derived here.
 # See issue #31.
 AGENTS_JSON="${SCRIPTS:-$(dirname -- "$0")}/agents.json"
 CLOUD_MODELS=$(jq -r '[.[] | .model | select(startswith("ollama-cloud/")) | sub("^ollama-cloud/";"")] | map({(.):{}}) | add // {}' "$AGENTS_JSON")