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/checkbox.tsx

@@ -1,76 +1,32 @@
-import * as React from "react"
-import { Checkbox as CheckboxPrimitive } from "@base-ui/react/checkbox"
-import { cn } from "../core/cn"
+import { Checkbox as MantineCheckbox } from "@mantine/core"
 
-interface CheckboxProps extends CheckboxPrimitive.Root.Props {
+interface CheckboxProps {
   label?: string
   indeterminate?: boolean
   className?: string
   labelClassName?: string
+  checked?: boolean
+  defaultChecked?: boolean
+  disabled?: boolean
+  onCheckedChange?: (checked: boolean) => void
+  id?: string
 }
 
-function Checkbox({ className, label, id, indeterminate, ...props }: CheckboxProps) {
-  const internalId = React.useId()
-  const checkboxId = id ?? internalId
-
+function Checkbox({ className, label, id, indeterminate, checked, defaultChecked, disabled, onCheckedChange, ...props }: CheckboxProps) {
   return (
-    <div className="flex items-center gap-2">
-      <CheckboxPrimitive.Root
-        id={checkboxId}
-        data-slot="checkbox"
-        className={cn(
-          "peer size-4 shrink-0 rounded border border-input bg-transparent transition-colors outline-none",
-          "focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50",
-          "data-checked:border-primary data-checked:bg-primary data-checked:text-primary-foreground",
-          "data-indeterminate:border-primary data-indeterminate:bg-primary data-indeterminate:text-primary-foreground",
-          "disabled:pointer-events-none disabled:opacity-50",
-          className
-        )}
-        indeterminate={indeterminate}
-        {...props}
-      >
-        <CheckboxPrimitive.Indicator
-          data-slot="checkbox-indicator"
-          className="flex items-center justify-center text-current"
-        >
-          {indeterminate ? (
-            <svg
-              xmlns="http://www.w3.org/2000/svg"
-              viewBox="0 0 24 24"
-              fill="none"
-              stroke="currentColor"
-              strokeWidth="3"
-              strokeLinecap="round"
-              className="size-3"
-            >
-              <line x1="5" y1="12" x2="19" y2="12" />
-            </svg>
-          ) : (
-            <svg
-              xmlns="http://www.w3.org/2000/svg"
-              viewBox="0 0 24 24"
-              fill="none"
-              stroke="currentColor"
-              strokeWidth="3"
-              strokeLinecap="round"
-              strokeLinejoin="round"
-              className="size-3"
-            >
-              <polyline points="20 6 9 17 4 12" />
-            </svg>
-          )}
-        </CheckboxPrimitive.Indicator>
-      </CheckboxPrimitive.Root>
-      {label && (
-        <label
-          htmlFor={checkboxId}
-          data-slot="checkbox-label"
-          className="text-sm font-medium leading-none peer-disabled:cursor-not-allowed peer-disabled:opacity-50 cursor-pointer select-none"
-        >
-          {label}
-        </label>
-      )}
-    </div>
+    <MantineCheckbox
+      id={id}
+      data-slot="checkbox"
+      label={label}
+      indeterminate={indeterminate}
+      checked={checked}
+      defaultChecked={defaultChecked}
+      disabled={disabled}
+      onChange={(event) => onCheckedChange?.(event.currentTarget.checked)}
+      className={className}
+      size="sm"
+      {...props}
+    />
   )
 }