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/components/FileUpload.tsx

@@ -0,0 +1,98 @@
+'use client';
+
+import { useState, useRef } from 'react';
+import { Button } from '@/components/ui/button';
+import { Upload } from 'lucide-react';
+
+interface FileUploadProps {
+  onUploadSuccess: () => void;
+}
+
+export default function FileUpload({ onUploadSuccess }: FileUploadProps) {
+  const [isUploading, setIsUploading] = useState(false);
+  const [message, setMessage] = useState<{ type: 'success' | 'error'; text: string } | null>(null);
+  const fileInputRef = useRef<HTMLInputElement>(null);
+
+  const handleFileChange = async (e: React.ChangeEvent<HTMLInputElement>) => {
+    const file = e.target.files?.[0];
+    if (!file) return;
+
+    setIsUploading(true);
+    setMessage(null);
+
+    const formData = new FormData();
+    formData.append('file', file);
+
+    try {
+      const response = await fetch('/api/upload', {
+        method: 'POST',
+        body: formData,
+      });
+
+      const data = await response.json();
+
+      if (response.ok) {
+        setMessage({
+          type: 'success',
+          text: `Successfully uploaded ${data.count} candle records`,
+        });
+        onUploadSuccess();
+      } else {
+        setMessage({
+          type: 'error',
+          text: data.error || 'Upload failed',
+        });
+      }
+    } catch (error: any) {
+      setMessage({
+        type: 'error',
+        text: error.message || 'Upload failed',
+      });
+    } finally {
+      setIsUploading(false);
+      // Reset file input
+      if (fileInputRef.current) {
+        fileInputRef.current.value = '';
+      }
+    }
+  };
+
+  return (
+    <div className="mb-4 p-4 bg-secondary/50 rounded-lg border border-border">
+      <h3 className="text-sm font-semibold mb-2">Upload CSV Data</h3>
+
+      <input
+        ref={fileInputRef}
+        type="file"
+        accept=".csv"
+        onChange={handleFileChange}
+        disabled={isUploading}
+        className="hidden"
+        id="csv-upload"
+      />
+
+      <Button
+        variant="outline"
+        size="sm"
+        className="w-full"
+        onClick={() => fileInputRef.current?.click()}
+        disabled={isUploading}
+      >
+        <Upload className="w-4 h-4 mr-2" />
+        {isUploading ? 'Uploading...' : 'Choose CSV File'}
+      </Button>
+
+      {message && (
+        <div
+          className={`mt-2 text-xs p-2 rounded ${
+            message.type === 'success'
+              ? 'bg-green-500/10 text-green-500 border border-green-500/20'
+              : 'bg-red-500/10 text-red-500 border border-red-500/20'
+          }`}
+        >
+          {message.text}
+        </div>
+      )}
+    </div>
+  );
+}