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/SvgOverlay.tsx

@@ -13,6 +13,7 @@ interface Annotation {
     endTime?: number;
     endPrice?: number;
   } | null;
+  color?: string;
   created_at: number;
 }
 
@@ -21,6 +22,7 @@ interface SvgOverlayProps {
   series: ISeriesApi<'Candlestick'> | null;
   activeTool: string | null;
   onAnnotationChange?: () => void;
+  selectedColor: string;
 }
 
 interface Point {
@@ -33,6 +35,7 @@ export default function SvgOverlay({
   series,
   activeTool,
   onAnnotationChange,
+  selectedColor,
 }: SvgOverlayProps) {
   const svgRef = useRef<SVGSVGElement>(null);
   const [dimensions, setDimensions] = useState({ width: 0, height: 0 });
@@ -169,6 +172,7 @@ export default function SvgOverlay({
             body: JSON.stringify({
               timestamp: drawingLine.start.time,
               label_type: 'line',
+              color: selectedColor,
               geometry: {
                 startTime: drawingLine.start.time,
                 startPrice: drawingLine.start.price,
@@ -299,7 +303,7 @@ export default function SvgOverlay({
           y1={start.y}
           x2={end.x}
           y2={end.y}
-          stroke="#3b82f6"
+          stroke={annotation.color || '#3b82f6'}
           strokeWidth="2"
           style={{ cursor: activeTool === 'delete' ? 'pointer' : 'default' }}
         />
@@ -322,7 +326,7 @@ export default function SvgOverlay({
         y1={start.y}
         x2={end.x}
         y2={end.y}
-        stroke="#3b82f6"
+        stroke={selectedColor}
         strokeWidth="2"
         strokeDasharray="5,5"
         opacity="0.6"