refactor: migrate frontend from shadcn/Tailwind to Mantine v9

Reescribe todos los componentes UI para usar Mantine v9 en lugar de shadcn/Tailwind.
Elimina cn(), CVA, components.json, theme_provider custom y globals.css con Tailwind.
Añade 25+ componentes nuevos (AppShell, AuthForm, DatePickerInput, Dropzone, etc.)
y MantineProvider como wrapper estándar del sistema de temas.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/functions/ui/alert.tsx

@@ -1,34 +1,70 @@
-import * as React from "react"
-import { cva, type VariantProps } from "class-variance-authority"
-import { cn } from "../core/cn"
+import * as React from 'react'
+import { Alert as MantineAlert, Box, Text } from '@mantine/core'
 
-const alertVariants = cva(
-  "group/alert relative grid w-full gap-0.5 rounded-lg border px-2.5 py-2 text-left text-sm has-data-[slot=alert-action]:relative has-data-[slot=alert-action]:pr-18 has-[>svg]:grid-cols-[auto_1fr] has-[>svg]:gap-x-2 *:[svg]:row-span-2 *:[svg]:translate-y-0.5 *:[svg]:text-current *:[svg:not([class*='size-'])]:size-4",
-  {
-    variants: {
-      variant: {
-        default: "bg-card text-card-foreground",
-        destructive: "bg-card text-destructive *:data-[slot=alert-description]:text-destructive/90 *:[svg]:text-current",
-      },
-    },
-    defaultVariants: { variant: "default" },
-  }
-)
+type AlertVariant = 'default' | 'destructive'
 
-function Alert({ className, variant, ...props }: React.ComponentProps<"div"> & VariantProps<typeof alertVariants>) {
-  return <div data-slot="alert" role="alert" className={cn(alertVariants({ variant }), className)} {...props} />
+const variantColorMap: Record<AlertVariant, string | undefined> = {
+  default: undefined,
+  destructive: 'red',
 }
 
-function AlertTitle({ className, ...props }: React.ComponentProps<"div">) {
-  return <div data-slot="alert-title" className={cn("font-medium group-has-[>svg]/alert:col-start-2 [&_a]:underline [&_a]:underline-offset-3 [&_a]:hover:text-foreground", className)} {...props} />
+function Alert({
+  className,
+  variant = 'default',
+  children,
+  ...props
+}: React.ComponentProps<'div'> & { variant?: AlertVariant }) {
+  return (
+    <MantineAlert
+      data-slot="alert"
+      color={variantColorMap[variant]}
+      radius="md"
+      variant="light"
+      className={className}
+      {...props}
+    >
+      {children}
+    </MantineAlert>
+  )
 }
 
-function AlertDescription({ className, ...props }: React.ComponentProps<"div">) {
-  return <div data-slot="alert-description" className={cn("text-sm text-balance text-muted-foreground md:text-pretty [&_a]:underline [&_a]:underline-offset-3 [&_a]:hover:text-foreground [&_p:not(:last-child)]:mb-4", className)} {...props} />
+function AlertTitle({ className, ...props }: React.ComponentProps<'div'>) {
+  return (
+    <Text
+      component="div"
+      data-slot="alert-title"
+      fw={500}
+      size="sm"
+      className={className}
+      {...props}
+    />
+  )
 }
 
-function AlertAction({ className, ...props }: React.ComponentProps<"div">) {
-  return <div data-slot="alert-action" className={cn("absolute top-2 right-2", className)} {...props} />
+function AlertDescription({ className, ...props }: React.ComponentProps<'div'>) {
+  return (
+    <Text
+      component="div"
+      data-slot="alert-description"
+      size="sm"
+      c="dimmed"
+      className={className}
+      {...props}
+    />
+  )
 }
 
+function AlertAction({ className, style, ...props }: React.ComponentProps<'div'>) {
+  return (
+    <Box
+      data-slot="alert-action"
+      style={{ position: 'absolute', top: 'var(--mantine-spacing-xs)', right: 'var(--mantine-spacing-xs)', ...style }}
+      className={className}
+      {...props}
+    />
+  )
+}
+
+const alertVariants = {} as const
+
 export { Alert, AlertTitle, AlertDescription, AlertAction, alertVariants }