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

src/app/page.tsx

@@ -512,18 +512,12 @@ export default function Home() {
         throw new Error('No candles found for this chart');
       }
 
-      const startTime = candlesData[0].time;
-      const endTime = candlesData[candlesData.length - 1].time;
-
-      // Make batch prediction request
-      const response = await fetch('/api/predict/batch', {
+      // Use regular predict endpoint with all candles from the database
+      const response = await fetch('/api/predict', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({
-          pair: chartData.name,
-          timeframe: '1h', // TODO: Get from chart metadata
-          start_time: startTime,
-          end_time: endTime,
+          candles: candlesData,
         }),
       });