feat: add DeepSeek provider support for claude-code-router

- Add DeepSeek provider config with Together.ai and official API support
- Configure deepseek and enhancetool transformers for reliable tool calling
- Add DEEPSEEK_API_KEY and DEEPSEEK_API_BASE env vars to docker-compose
- Update shannon CLI to recognize DeepSeek as valid router provider

configs/router-config.json

@@ -23,6 +23,15 @@
       "transformer": {
         "use": ["gemini"]
       }
+    },
+    {
+      "name": "deepseek",
+      "api_base_url": "$DEEPSEEK_API_BASE",
+      "api_key": "$DEEPSEEK_API_KEY",
+      "models": ["deepseek-ai/DeepSeek-V3", "deepseek-ai/DeepSeek-R1", "deepseek-chat", "deepseek-reasoner"],
+      "transformer": {
+        "use": ["deepseek", "enhancetool"]
+      }
     }
   ],
   "Router": {