fix: align opencode-zen provider setup

src/agents/model-selection.ts

@@ -24,6 +24,7 @@ export function modelKey(provider: string, model: string) {
 export function normalizeProviderId(provider: string): string {
   const normalized = provider.trim().toLowerCase();
   if (normalized === "z.ai" || normalized === "z-ai") return "zai";
+  if (normalized === "opencode-zen") return "opencode";
   return normalized;
 }