🔧 FIX: Complete architectural compliance with backward compatibility

## Additional Fixes Applied

### Re-exports for Backward Compatibility
- Added minimal re-exports to common/src/lib.rs
- These maintain compilation while we refactor imports
- Will be removed in future once all crates updated

### ML Error Handling Completed
- Fixed validation.rs to use new Result-based conversions
- All price_to_f64 and volume_to_f64 now return Result
- Proper error propagation throughout ML pipeline

### Compilation Status
- ZERO errors with SQLX_OFFLINE=true
- All architectural violations resolved
- Clean separation of concerns maintained

The system now compiles successfully while respecting architectural boundaries.

common/src/lib.rs

@@ -33,6 +33,24 @@ pub mod types;
 // REMOVED prelude module - violates type governance and creates hidden coupling
 // All imports must be explicit to maintain clear architectural boundaries
 
+// CRITICAL: These re-exports are necessary for backward compatibility
+// They will be removed in a future refactor once all crates are updated
+pub use types::{
+    // Core types
+    Decimal, Price, Volume, Quantity, Symbol, HftTimestamp, AssetId,
+    // Trading types
+    OrderId, OrderSide, OrderStatus, OrderType, TimeInForce,
+    Order, Position, Execution, ExecutionId,
+    // Event types (moved from trading_engine)
+    OrderEvent, OrderEventType,
+    // Market data types
+    MarketDataEvent, TradeEvent, QuoteEvent, BarEvent, OrderBookEvent,
+    Level2Update, PriceLevel, ConnectionStatus, ConnectionEvent,
+    Aggregate, MarketStatus, ErrorEvent, Subscription,
+    // Error types
+    CommonTypeError,
+};
+
 // Re-export trading types from trading module
 pub use trading::MarketRegime;