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.

openspec/changes/candle-backend/tasks.md

@@ -86,11 +86,11 @@
 
 ## 10. Prediction UI — Chart Rendering
 
-- [ ] 10.1 Add histogram series to CandleChart for prediction rendering — per-bar colors from label config at 10-20% opacity
-- [ ] 10.2 Add series markers for prediction span labels — show `{label} ({confidence}%)` below bars at span start
-- [ ] 10.3 Implement confidence threshold filtering — only render predictions above threshold
-- [ ] 10.4 Implement label type filtering — toggle visibility per label from PredictionPanel checkboxes
-- [ ] 10.5 Implement prediction layer visibility toggle — show/hide histogram series and markers
+- [x] 10.1 Add histogram series to CandleChart for prediction rendering — per-bar colors from label config at 10-20% opacity
+- [x] 10.2 Add series markers for prediction span labels — show `{label} ({confidence}%)` below bars at span start
+- [x] 10.3 Implement confidence threshold filtering — only render predictions above threshold
+- [x] 10.4 Implement label type filtering — toggle visibility per label from PredictionPanel checkboxes
+- [x] 10.5 Implement prediction layer visibility toggle — show/hide histogram series and markers
 
 ## 11. Prediction UI — Disagreements & Feedback