feat(notifications): add multi-channel notification module with Email, FCM, templates, and event listeners

- Domain: NotificationLog/NotificationPreference entities, repositories, channel value object
- Infrastructure: EmailService (nodemailer/SMTP), FcmService (firebase-admin), TemplateService (Handlebars)
- Application: SendNotification CQRS command, UserRegistered + AgentVerified event listeners
- Presentation: NotificationsController with history, preferences, and templates endpoints
- Prisma: NotificationLog and NotificationPreference models with proper indexes
- Templates: Vietnamese notification templates for user.registered, agent.verified, listing.approved, inquiry.received, password.reset

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/components/ui/button.tsx

@@ -0,0 +1,44 @@
+import * as React from 'react';
+import { cva, type VariantProps } from 'class-variance-authority';
+import { cn } from '@/lib/utils';
+
+const buttonVariants = cva(
+  'inline-flex items-center justify-center whitespace-nowrap rounded-md text-sm font-medium ring-offset-background transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:pointer-events-none disabled:opacity-50',
+  {
+    variants: {
+      variant: {
+        default: 'bg-primary text-primary-foreground hover:bg-primary/90',
+        destructive: 'bg-destructive text-destructive-foreground hover:bg-destructive/90',
+        outline: 'border border-input bg-background hover:bg-accent hover:text-accent-foreground',
+        secondary: 'bg-secondary text-secondary-foreground hover:bg-secondary/80',
+        ghost: 'hover:bg-accent hover:text-accent-foreground',
+        link: 'text-primary underline-offset-4 hover:underline',
+      },
+      size: {
+        default: 'h-10 px-4 py-2',
+        sm: 'h-9 rounded-md px-3',
+        lg: 'h-11 rounded-md px-8',
+        icon: 'h-10 w-10',
+      },
+    },
+    defaultVariants: {
+      variant: 'default',
+      size: 'default',
+    },
+  },
+);
+
+export interface ButtonProps
+  extends React.ButtonHTMLAttributes<HTMLButtonElement>,
+    VariantProps<typeof buttonVariants> {}
+
+const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
+  ({ className, variant, size, ...props }, ref) => {
+    return (
+      <button className={cn(buttonVariants({ variant, size, className }))} ref={ref} {...props} />
+    );
+  },
+);
+Button.displayName = 'Button';
+
+export { Button, buttonVariants };