fix(api): add GET /api/charts/[id] and fix batch prediction

- Add GET handler to /api/charts/[id] route to fetch chart metadata
- Fix batch prediction to use regular /predict endpoint with database candles
- Remove /predict/batch usage (was designed for file-based predictions)
- Make volume field optional in CandleData model (database candles don't have volume)
- Convert timestamps to ISO dates for batch requests

Known issue: TA-Lib indicators failing with 'input array type is not double'
- May need to ensure candle data is float64/double type before processing

services/ml/app/main.py

@@ -66,7 +66,7 @@ class CandleData(BaseModel):
     high: float
     low: float
     close: float
-    volume: float
+    volume: Optional[float] = None
 
 
 class PredictRequest(BaseModel):