feat: create UI shell and components

- Toolbox component with tool selection (break up/down, line, delete)
- FileUpload component with CSV upload functionality
- Main page layout with sidebar and chart area
- Tool state management and export functionality

src/app/page.tsx

@@ -1,10 +1,45 @@
+'use client';
+
+import { useState } from 'react';
+import Toolbox, { Tool } from '@/components/Toolbox';
+import FileUpload from '@/components/FileUpload';
+
 export default function Home() {
+  const [activeTool, setActiveTool] = useState<Tool>(null);
+
+  const handleExport = () => {
+    window.location.href = '/api/export';
+  };
+
+  const handleUploadSuccess = () => {
+    // TODO: Trigger chart refresh
+    console.log('Upload successful - refresh chart');
+  };
+
   return (
-    <main className="min-h-screen p-8">
-      <h1 className="text-2xl font-bold">Candle Annotator</h1>
-      <p className="mt-4 text-slate-400">
-        Upload CSV data and annotate candlestick charts
-      </p>
-    </main>
+    <div className="flex h-screen">
+      {/* Sidebar */}
+      <aside className="flex flex-col">
+        <div className="p-4 border-b border-border">
+          <h1 className="text-xl font-bold">Candle Annotator</h1>
+        </div>
+        <div className="p-4">
+          <FileUpload onUploadSuccess={handleUploadSuccess} />
+        </div>
+        <Toolbox
+          activeTool={activeTool}
+          onToolChange={setActiveTool}
+          onExport={handleExport}
+        />
+      </aside>
+
+      {/* Main chart area */}
+      <main className="flex-1 flex items-center justify-center bg-background">
+        <div className="text-muted-foreground text-center">
+          <p className="text-lg">Upload a CSV file to view the candlestick chart</p>
+          <p className="text-sm mt-2">CSV format: time, open, high, low, close</p>
+        </div>
+      </main>
+    </div>
   );
 }