feat: add claude-code-router support for multi-model testing

- Add ROUTER=true flag to route requests through claude-code-router
- Add router service to docker-compose with profile-based activation
- Support OpenAI (gpt-4o) and Google Gemini (gemini-2.5-pro) as alternatives
- Add router-config.json with provider configuration template
- Update .env.example with provider API key options
- Document router mode limitations (cost tracking shows $0)

.env.example

@@ -1,8 +1,33 @@
 # Shannon Environment Configuration
 # Copy this file to .env and fill in your credentials
 
-# Anthropic API Key (required - choose one)
+# Recommended output token configuration for larger tool outputs
+CLAUDE_CODE_MAX_OUTPUT_TOKENS=64000
+
+# =============================================================================
+# OPTION 1: Direct Anthropic (default, no router)
+# =============================================================================
 ANTHROPIC_API_KEY=your-api-key-here
 
 # OR use OAuth token instead
 # CLAUDE_CODE_OAUTH_TOKEN=your-oauth-token-here
+
+# =============================================================================
+# OPTION 2: Router Mode (use alternative providers)
+# =============================================================================
+# Enable router mode by running: ./shannon start ... ROUTER=true
+# Then configure ONE of the providers below:
+
+# --- OpenAI ---
+# OPENAI_API_KEY=sk-your-openai-key
+# ROUTER_DEFAULT=openai,gpt-4o
+
+# --- Google Gemini ---
+GEMINI_API_KEY=your-gemini-key
+ROUTER_DEFAULT=gemini,gemini-2.5-pro
+
+# =============================================================================
+# Available Models
+# =============================================================================
+# OpenAI:  gpt-4o, gpt-4o-mini
+# Gemini:  gemini-2.5-pro, gemini-2.5-flash