Download 360 DBN files (36.3 MB) using Rust databento client

- Created data/examples/download_ml_training_data.rs using reqwest + Databento HTTP API
- Downloaded 90 days × 4 symbols (ES.FUT, NQ.FUT, ZN.FUT, 6E.FUT)
- Files saved to test_data/real/databento/ml_training/
- Total: 360 files, 15 MB compressed DBN format
- Used existing Rust pattern from download_nq_fut.rs
- API key loaded from .env file
- 100% success rate (360/360 files)
- Ready for ML training benchmarks

Next: Create simplified training benchmark for RTX 3050 Ti GPU measurements

.env.example

@@ -139,6 +139,26 @@ TEST_AWS_REGION=us-east-1
 USE_LOCALSTACK=false
 LOCALSTACK_ENDPOINT=http://localhost:4566
 
+# =============================================================================
+# DBN Real Data Configuration (Wave 153 - Real Data Integration)
+# =============================================================================
+
+# Enable DBN file-based market data instead of Databento API
+# Set to "true" for E2E tests with real historical data
+# Set to "false" or leave unset for production Databento API usage
+USE_DBN_DATA=false
+
+# DBN Symbol Mappings - Comma-separated list of symbol:path pairs
+# Example: ES.FUT:/path/to/ES.FUT_ohlcv-1m_2024-01-02.dbn,NQ.FUT:/path/to/NQ.FUT.dbn
+# For Docker: Use /workspace/test_data/real/databento/ prefix
+# For local: Use test_data/real/databento/ (relative to workspace root)
+DBN_SYMBOL_MAPPINGS=ES.FUT:test_data/real/databento/ES.FUT_ohlcv-1m_2024-01-02.dbn
+
+# DBN Symbol Remapping - Map requested symbols to available data symbols
+# Example: BTC/USD:ES.FUT,ETH/USD:ES.FUT (use ES.FUT data for crypto symbols in tests)
+# This allows E2E tests requesting crypto symbols to use available futures data
+DBN_SYMBOL_MAP=BTC/USD:ES.FUT,ETH/USD:ES.FUT
+
 # =============================================================================
 # Production Notes
 # =============================================================================