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/dashboard_layout.tsx

@@ -1,5 +1,5 @@
 import * as React from 'react'
-import { cn } from '../core/cn'
+import { SimpleGrid, Paper, Text } from '@mantine/core'
 
 interface DashboardWidget {
   id: string
@@ -16,51 +16,37 @@ interface DashboardLayoutProps {
   className?: string
 }
 
-const gapClasses = { sm: 'gap-2', md: 'gap-4', lg: 'gap-6' }
-
-const spanClasses: Record<number, string> = {
-  1: 'col-span-1',
-  2: 'col-span-1 md:col-span-2',
-  3: 'col-span-1 md:col-span-2 lg:col-span-3',
-  4: 'col-span-1 md:col-span-2 lg:col-span-4',
-}
-
-const rowSpanClasses: Record<number, string> = {
-  1: 'row-span-1',
-  2: 'row-span-2',
-}
+const gapMap = { sm: 'xs', md: 'md', lg: 'lg' } as const
 
 export function dashboardLayout({
   widgets,
   columns = 4,
   gap = 'md',
-  className,
 }: DashboardLayoutProps): React.ReactElement {
-  const gridCols: Record<number, string> = {
-    1: 'grid-cols-1',
-    2: 'grid-cols-1 md:grid-cols-2',
-    3: 'grid-cols-1 md:grid-cols-2 lg:grid-cols-3',
-    4: 'grid-cols-1 md:grid-cols-2 lg:grid-cols-4',
-  }
-
   return (
-    <div className={cn('grid', gridCols[columns], gapClasses[gap], className)}>
+    <SimpleGrid
+      cols={{ base: 1, md: Math.min(columns, 2), lg: columns }}
+      spacing={gapMap[gap]}
+    >
       {widgets.map((widget) => (
-        <div
+        <Paper
           key={widget.id}
-          className={cn(
-            'rounded-xl border bg-card p-4 text-card-foreground shadow-sm',
-            spanClasses[widget.span || 1],
-            rowSpanClasses[widget.rowSpan || 1]
-          )}
+          p="md"
+          withBorder
+          shadow="xs"
+          radius="md"
+          style={{
+            gridColumn: widget.span && widget.span > 1 ? `span ${widget.span}` : undefined,
+            gridRow: widget.rowSpan === 2 ? 'span 2' : undefined,
+          }}
         >
           {widget.title && (
-            <h3 className="mb-3 text-sm font-medium text-muted-foreground">{widget.title}</h3>
+            <Text size="sm" fw={500} c="dimmed" mb="sm">{widget.title}</Text>
           )}
           {widget.content}
-        </div>
+        </Paper>
       ))}
-    </div>
+    </SimpleGrid>
   )
 }