added opencode zen as provider

docs/configuration.md

@@ -47,6 +47,14 @@ OPENROUTER_API_KEY=your_openrouter_api_key_here
 # If using OpenRouter, comment out native API keys above
 ```
 
+**Option 2.5: OpenCode Zen (Curated coding models)**
+```env
+# OpenCode Zen for tested and verified coding models
+ZEN_API_KEY=your_zen_api_key_here
+# Get from: https://opencode.ai/auth
+# Provides access to models optimized for coding agents
+```
+
 **Option 3: Custom API Endpoints (Local models)**
 ```env
 # For Ollama, vLLM, LM Studio, etc.