task 9.7: replace duplicate interfaces with @/types imports

Replace locally-defined duplicate interfaces in page.tsx,
CandleChart.tsx, SpanAnnotationManager.tsx, Toolbox.tsx,
SpanAnnotationList.tsx, and SpanPopover.tsx with imports from @/types.

- SpanAnnotation, SpanLabelType: replaced in all 6 files
- Candle, AnnotationType: replaced in CandleChart.tsx, SpanAnnotationManager.tsx, Toolbox.tsx
- Annotation (with geometry): replaced in CandleChart.tsx and Toolbox.tsx
- Chart: kept local in page.tsx (shared type has created_at: Date|number vs local number)
- Annotation in page.tsx: kept local (geometry: any) but added missing color field for compatibility

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/SpanAnnotationManager.tsx

@@ -4,39 +4,9 @@ import { useEffect, useState, useRef, useCallback } from 'react';
 import { IChartApi, ISeriesApi, Time } from 'lightweight-charts';
 import { SpanRectanglePrimitive, SpanData } from './SpanRectanglePrimitive';
 import SpanPopover from './SpanPopover';
+import type { Candle, SpanAnnotation, SpanLabelType } from '@/types';
 
-interface Candle {
-  time: number;
-  open: number;
-  high: number;
-  low: number;
-  close: number;
-}
-
-interface SpanAnnotation {
-  id: number;
-  chart_id: number;
-  start_time: number;
-  end_time: number;
-  label: string;
-  confidence: number | null;
-  outcome: string | null;
-  notes: string | null;
-  sub_spans: any;
-  color: string;
-  created_at: number;
-}
-
-interface SpanLabelType {
-  id: number;
-  name: string;
-  display_name: string;
-  color: string;
-  hotkey: string | null;
-  is_active: boolean;
-  sort_order: number;
-  created_at: number;
-}
+// Candle, SpanAnnotation, SpanLabelType are imported from @/types above.
 
 interface SpanAnnotationManagerProps {
   chart: IChartApi | null;