feat(ui): add prediction chart rendering with histogram overlay, markers, filtering, and visibility toggle

- Add histogram series to CandleChart for per-bar prediction colors (15% opacity)
- Add series markers showing label name and confidence % at prediction span starts
- Implement confidence threshold filtering for both histogram and markers
- Implement label type filtering from PredictionPanel checkboxes
- Implement prediction layer visibility toggle (show/hide)
- Add getVisibleCandles method to CandleChartHandle for on-demand prediction fetching
- Pass prediction state props from page.tsx to CandleChart

Tasks 10.1-10.5 complete.

src/app/page.tsx

@@ -573,6 +573,12 @@ export default function Home() {
           selectedSpanId={selectedSpanId}
           onSpanAnnotationsChange={handleSpanAnnotationsChange}
           onSelectedSpanChange={handleSelectedSpanChange}
+          predictionVisible={predictionState.visible}
+          perCandlePredictions={predictionState.perCandlePredictions}
+          predictionSpans={predictionState.spans}
+          confidenceThreshold={predictionState.confidenceThreshold}
+          selectedLabels={predictionState.selectedLabels}
+          modelInfo={predictionState.modelInfo}
         />
       </main>
     </div>