fix: add opencode-zen to PROVIDER_MODELS_CONFIG (#667)

The 'Import from /models' button failed because opencode-zen was not
registered in PROVIDER_MODELS_CONFIG. The provider's API at
https://opencode.ai/zen/v1/models returns standard OpenAI-compatible
format and is now properly configured for model import.

src/app/api/providers/[id]/models/route.ts

@@ -318,6 +318,14 @@ const PROVIDER_MODELS_CONFIG: Record<string, ProviderModelsConfigEntry> = {
     authPrefix: "Bearer ",
     parseResponse: (data) => data.data || data.models || [],
   },
+  "opencode-zen": {
+    url: "https://opencode.ai/zen/v1/models",
+    method: "GET",
+    headers: { "Content-Type": "application/json" },
+    authHeader: "Authorization",
+    authPrefix: "Bearer ",
+    parseResponse: (data) => data.data || data.models || [],
+  },
 };
 
 /**