fix(ml): make pair and timeframe optional in PredictRequest

- Change pair and timeframe fields from required to optional
- Frontend only sends candles array, not pair/timeframe metadata
- These fields are only used for logging, not prediction logic
- Update logging to handle None values with 'unknown' fallback
- Fixes 422 validation error on /predict endpoint

services/ml/app/main.py

@@ -71,8 +71,8 @@ class CandleData(BaseModel):
 
 class PredictRequest(BaseModel):
     """Request model for /predict endpoint."""
-    pair: str = Field(..., description="Trading pair (e.g., EURUSD)")
-    timeframe: str = Field(..., description="Timeframe (e.g., 1H, 4H, 1D)")
+    pair: Optional[str] = Field(None, description="Trading pair (e.g., EURUSD)")
+    timeframe: Optional[str] = Field(None, description="Timeframe (e.g., 1H, 4H, 1D)")
     candles: List[CandleData] = Field(..., min_length=1, description="Array of candle data")
 
 
@@ -518,7 +518,7 @@ async def predict(request: PredictRequest):
             detail="Pipeline configuration not loaded"
         )
     
-    logger.info(f"Predict request: {request.pair} {request.timeframe}, {len(request.candles)} candles")
+    logger.info(f"Predict request: {request.pair or 'unknown'} {request.timeframe or 'unknown'}, {len(request.candles)} candles")
     
     try:
         # Convert candles to list of dicts