fix(agents): rename xai provider key to xai-oc to avoid opencode catalog collision (#118)

opencode ships a built-in `xai` model-catalog entry (a real @ai-sdk/xai
integration with Responses-API support). Naming our custom OpenAI-compatible
shim `xai` too made opencode's --auto permission-check path assume the
catalog's provider object once a `permission` block is present (always, in
this pipeline) and call .responses(), which our shim doesn't implement —
crashing every @lead/@ops run with "Z.responses is not a function".

Reproduced locally with the production config shape on opencode 1.17.13;
renaming the provider key to xai-oc (model id xai-oc/grok-4.5) fixes it
reliably across repeated fresh-state runs.

.gitea/workflows/scripts/build-activity-log.sh

@@ -38,7 +38,7 @@ COST=${COST:-0}; INP=${INP:-0}; OUT=${OUT:-0}; CR=${CR:-0}; CW=${CW:-0}; RE=${RE
 IN_TOTAL=$(( INP + CR + CW ))                          # total input context processed
 # Cost label: ollama / ollama-cloud models are SUBSCRIPTION-billed (GPU-time against the plan, no
 # $/token price exists), so a "$0.0000" there would be misleading — label it a subscription instead.
-# Metered providers (xai/…) get the real dollar cost opencode computed.
+# Metered providers (xai-oc/…) get the real dollar cost opencode computed.
 case "${MODEL:-}" in
   ollama*|*"/ollama"*) COSTF="subscription" ;;
   *) COSTF=$(awk -v c="$COST" 'BEGIN{printf "$%.4f", c+0}') ;;