chore(config): add .env.example for local development

- Provide template for API key configuration
- Include recommended test settings
- Document optional environment variables

.env.example

@@ -0,0 +1,15 @@
+# Anthropic API Configuration
+# Copy this file to .env and add your API key
+# Get your API key at: https://console.anthropic.com/settings/keys
+
+ANTHROPIC_API_KEY=sk-ant-api03-...
+
+# Optional: Default model for testing (recommended for cost savings)
+CLAUDE_MODEL=claude-3-5-haiku-latest
+
+# Optional: Test mode settings
+TEST_MODE=true
+MAX_TOKENS=10
+
+# Optional: Verbose output for debugging
+DEBUG=false