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/indicator.tsx

@@ -0,0 +1,39 @@
+import * as React from 'react'
+import { Indicator } from '@mantine/core'
+import type { MantineColor } from '@mantine/core'
+
+interface FnIndicatorProps {
+  children: React.ReactNode
+  color?: MantineColor
+  size?: number
+  position?: 'top-start' | 'top-center' | 'top-end' | 'middle-start' | 'middle-center' | 'middle-end' | 'bottom-start' | 'bottom-center' | 'bottom-end'
+  processing?: boolean
+  disabled?: boolean
+  label?: React.ReactNode
+}
+
+function FnIndicator({
+  children,
+  color = 'red',
+  size = 10,
+  position = 'top-end',
+  processing = false,
+  disabled = false,
+  label,
+}: FnIndicatorProps) {
+  return (
+    <Indicator
+      color={color}
+      size={size}
+      position={position}
+      processing={processing}
+      disabled={disabled}
+      label={label}
+    >
+      {children}
+    </Indicator>
+  )
+}
+
+export { FnIndicator }
+export type { FnIndicatorProps }