design: change to minimalistic and clean light theme

- Replace Matrix/terminal dark theme with modern light design
- Update Tailwind config with clean, professional color palette
- Change from monospace to Inter sans-serif font
- Update chart styling to use white background with subtle grids
- Remove glow effects and neon colors from buttons and UI
- Update color picker with better color options
- Improve sidebar spacing and typography
- Update annotation badges with softer colors
- Change scrollbar styling to match light theme

src/app/page.tsx

@@ -87,30 +87,33 @@ export default function Home() {
   }, [selectedLabelId]);
 
   return (
-    <div className="flex h-screen">
+    <div className="flex h-screen bg-background">
       {/* Sidebar */}
-      <aside className="w-64 flex-shrink-0 flex flex-col border-r border-border">
-        <div className="p-4 border-b border-border">
-          <h1 className="text-xl font-bold">Candle Annotator</h1>
+      <aside className="w-72 flex-shrink-0 flex flex-col border-r border-border bg-card">
+        <div className="p-6 border-b border-border">
+          <h1 className="text-2xl font-semibold text-foreground">Candle Annotator</h1>
+          <p className="text-sm text-muted-foreground mt-1">Chart annotation tool</p>
         </div>
-        <div className="p-4">
+        <div className="p-6">
           <FileUpload onUploadSuccess={handleUploadSuccess} />
         </div>
-        <Toolbox
-          activeTool={activeTool}
-          onToolChange={setActiveTool}
-          onExport={handleExport}
-          selectedColor={selectedColor}
-          onColorChange={setSelectedColor}
-          annotations={annotations}
-          selectedLabelId={selectedLabelId}
-          onLabelSelect={handleLabelSelect}
-          onLabelDelete={handleLabelDelete}
-        />
+        <div className="px-6 pb-6">
+          <Toolbox
+            activeTool={activeTool}
+            onToolChange={setActiveTool}
+            onExport={handleExport}
+            selectedColor={selectedColor}
+            onColorChange={setSelectedColor}
+            annotations={annotations}
+            selectedLabelId={selectedLabelId}
+            onLabelSelect={handleLabelSelect}
+            onLabelDelete={handleLabelDelete}
+          />
+        </div>
       </aside>
 
       {/* Main chart area */}
-      <main className="flex-1 relative">
+      <main className="flex-1 relative bg-background">
         <CandleChart
           ref={chartRef}
           activeTool={activeTool}