feat: add color support for line annotations

- Add color field to annotations schema with default blue (#3b82f6)
- Add color picker UI with 5 preset colors (red, green, blue, yellow, white)
- Pass selected color through component hierarchy (Page -> Toolbox, CandleChart -> SvgOverlay)
- Store color when creating line annotations
- Render lines with their stored color
- Update database with color column
- Preview lines show selected color during drawing

Phase 1 of LINE_DRAWING_IMPROVEMENTS.md complete

src/components/CandleChart.tsx

@@ -28,6 +28,7 @@ interface Annotation {
 interface CandleChartProps {
   activeTool: string | null;
   onAnnotationChange?: () => void;
+  selectedColor: string;
 }
 
 export interface CandleChartHandle {
@@ -35,7 +36,7 @@ export interface CandleChartHandle {
 }
 
 const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
-  ({ activeTool, onAnnotationChange }, ref) => {
+  ({ activeTool, onAnnotationChange, selectedColor }, ref) => {
     const chartContainerRef = useRef<HTMLDivElement>(null);
     const chartRef = useRef<IChartApi | null>(null);
     const seriesRef = useRef<ISeriesApi<'Candlestick'> | null>(null);
@@ -277,6 +278,7 @@ const CandleChart = forwardRef<CandleChartHandle, CandleChartProps>(
           series={seriesRef.current}
           activeTool={activeTool}
           onAnnotationChange={onAnnotationChange}
+          selectedColor={selectedColor}
         />
       </div>
     );