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/Select.tsx

@@ -0,0 +1,37 @@
+import type { SelectHTMLAttributes } from 'react';
+
+interface SelectOption {
+  value: string;
+  label: string;
+}
+
+interface SelectProps extends SelectHTMLAttributes<HTMLSelectElement> {
+  label?: string;
+  options: SelectOption[];
+  error?: string;
+}
+
+export const Select = ({ label, options, error, className = '', ...props }: SelectProps) => {
+  return (
+    <div className="w-full">
+      {label && (
+        <label className="block text-sm font-medium text-[#1b1b1d] mb-1">
+          {label}
+        </label>
+      )}
+      <select
+        className={`w-full px-3 py-2 bg-[#f5f3f5] border border-[#c5c6cd] rounded-md text-[#1b1b1d] focus:outline-none focus:ring-2 focus:ring-[#1B263B] focus:border-transparent transition-colors ${className}`}
+        {...props}
+      >
+        {options.map((option) => (
+          <option key={option.value} value={option.value}>
+            {option.label}
+          </option>
+        ))}
+      </select>
+      {error && (
+        <p className="mt-1 text-sm text-red-600">{error}</p>
+      )}
+    </div>
+  );
+};