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/skill-gitea-admin.sh

@@ -107,7 +107,7 @@ curl -sS -X POST -H "Authorization: token $SELF_TOKEN" "$API/orgs/{org}/labels"
 3. Commit the standard caller so it gets the agents — `PUT /repos/{owner}/{repo}/contents/.gitea/workflows/ai-agent.yml`
    with base64 `content`, `message`, `branch:"main"` (copy the exact caller from the `agents` repo README).
 4. Add the agent bot users as collaborators: `PUT /repos/{owner}/{repo}/collaborators/{username}` (`{"permission":"write"}`).
-5. Ensure the repo can run agents — the org must hold the runtime secrets (ANTHROPIC_API_KEY, SELF_TOKEN,
+5. Ensure the repo can run agents — the org must hold the runtime secrets (XAI_API_KEY, SELF_TOKEN,
    TOKEN_* , OLLAMA_URL, OLLAMA_CLOUD_API_KEY); set any missing via the secrets calls above.
 
 ## Packages / container registry