chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

frontend/src/components/ui/Modal.tsx

@@ -0,0 +1,44 @@
+import { X } from 'lucide-react';
+import type { ReactNode } from 'react';
+
+interface ModalProps {
+  isOpen: boolean;
+  onClose: () => void;
+  title: string;
+  children: ReactNode;
+  footer?: ReactNode;
+}
+
+export const Modal = ({ isOpen, onClose, title, children, footer }: ModalProps) => {
+  if (!isOpen) return null;
+  
+  return (
+    <div className="fixed inset-0 z-50 overflow-y-auto">
+      <div className="flex min-h-full items-center justify-center p-4 text-center">
+        <div 
+          className="fixed inset-0 bg-black/30 transition-opacity" 
+          onClick={onClose}
+        />
+        <div className="relative transform overflow-hidden rounded-lg bg-white text-left shadow-xl transition-all w-full max-w-lg">
+          <div className="flex items-center justify-between border-b border-[#e4e2e4] px-4 py-3">
+            <h3 className="text-lg font-semibold text-[#1b1b1d]">{title}</h3>
+            <button
+              onClick={onClose}
+              className="rounded-full p-1 hover:bg-[#f5f3f5] transition-colors"
+            >
+              <X size={20} className="text-[#75777d]" />
+            </button>
+          </div>
+          <div className="px-4 py-4">
+            {children}
+          </div>
+          {footer && (
+            <div className="border-t border-[#e4e2e4] px-4 py-3 flex justify-end gap-2">
+              {footer}
+            </div>
+          )}
+        </div>
+      </div>
+    </div>
+  );
+};