feat: implement email sending functionality via Resend service

app/components/ui/checkbox.tsx

@@ -0,0 +1,53 @@
+import React from "react"
+import { Check } from "lucide-react"
+import { cn } from "@/lib/utils"
+
+interface CheckboxProps {
+  id?: string
+  checked?: boolean
+  onChange?: (checked: boolean) => void
+  className?: string
+  disabled?: boolean
+}
+
+export const Checkbox: React.FC<CheckboxProps> = ({
+  id,
+  checked = false,
+  onChange,
+  className,
+  disabled = false
+}) => {
+  const handleChange = () => {
+    if (!disabled && onChange) {
+      onChange(!checked)
+    }
+  }
+
+  return (
+    <div 
+      className={cn(
+        "relative inline-flex items-center justify-center w-5 h-5 rounded border-2 cursor-pointer transition-all duration-200",
+        checked 
+          ? "bg-primary border-primary text-primary-foreground" 
+          : "bg-background border-input hover:border-primary/50",
+        disabled && "opacity-50 cursor-not-allowed",
+        className
+      )}
+      onClick={handleChange}
+    >
+      <input
+        type="checkbox"
+        id={id}
+        checked={checked}
+        onChange={() => {}} // Controlled by div onClick
+        className="sr-only"
+        disabled={disabled}
+      />
+      {checked && (
+        <Check 
+          className="w-3 h-3 text-current animate-in fade-in-0 scale-in-95 duration-200" 
+        />
+      )}
+    </div>
+  )
+}