docs: add DEPLOYMENT_MODE configuration to env example

.env.example

@@ -39,3 +39,15 @@ AUTO_DOWNLOAD_PRICE_DATA=true
 # Use relative paths (./volumes) or absolute paths (/home/user/ai-trader-volumes)
 # Defaults to current directory (.) if not set
 VOLUME_PATH=.
+
+# =============================================================================
+# Deployment Mode Configuration
+# =============================================================================
+# DEPLOYMENT_MODE controls AI model calls and data isolation
+# - PROD: Real AI API calls, uses data/agent_data/ and data/trading.db
+# - DEV: Mock AI responses, uses data/dev_agent_data/ and data/trading_dev.db
+DEPLOYMENT_MODE=PROD
+
+# Preserve dev data between runs (DEV mode only)
+# Set to true to keep dev database and files for debugging
+PRESERVE_DEV_DATA=false