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

docker-compose.yml

@@ -58,6 +58,8 @@ services:
       - ANTHROPIC_API_KEY=${ANTHROPIC_API_KEY:-}
       - OPENAI_API_KEY=${OPENAI_API_KEY:-}
       - GEMINI_API_KEY=${GEMINI_API_KEY:-}
+      - DEEPSEEK_API_KEY=${DEEPSEEK_API_KEY:-}
+      - DEEPSEEK_API_BASE=${DEEPSEEK_API_BASE:-https://api.together.xyz/v1/chat/completions}
       - ROUTER_DEFAULT=${ROUTER_DEFAULT:-openai,gpt-4o}
     healthcheck:
       test: ["CMD", "node", "-e", "require('http').get('http://localhost:3456/health', r => process.exit(r.statusCode === 200 ? 0 : 1)).on('error', () => process.exit(1))"]