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/input.tsx

@@ -1,18 +1,17 @@
-import * as React from "react"
-import { Input as InputPrimitive } from "@base-ui/react/input"
-import { cn } from "../core/cn"
+import * as React from 'react'
+import { TextInput, Box } from '@mantine/core'
 
-function Input({ className, type, ...props }: React.ComponentProps<"input">) {
+function Input({
+  className,
+  type,
+  ...props
+}: React.ComponentProps<typeof TextInput> & { type?: string }) {
   return (
-    <InputPrimitive
+    <TextInput
       type={type}
       data-slot="input"
-      className={cn(
-        "h-8 w-full min-w-0 rounded-lg border border-input bg-transparent px-2.5 py-1 text-base transition-colors outline-none file:inline-flex file:h-6 file:border-0 file:bg-transparent file:text-sm file:font-medium file:text-foreground placeholder:text-muted-foreground focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50 disabled:pointer-events-none disabled:cursor-not-allowed disabled:bg-input/50 disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-3 aria-invalid:ring-destructive/20 md:text-sm dark:bg-input/30 dark:disabled:bg-input/80 dark:aria-invalid:border-destructive/50 dark:aria-invalid:ring-destructive/40",
-        "group-has-[data-slot=input-icon-start]/input-group:pl-9",
-        "group-has-[data-slot=input-icon-end]/input-group:pr-9",
-        className
-      )}
+      size="sm"
+      className={className}
       {...props}
     />
   )
@@ -25,32 +24,34 @@ interface InputGroupProps {
 
 function InputGroup({ children, className }: InputGroupProps) {
   return (
-    <div data-slot="input-group" className={cn("group/input-group relative", className)}>
+    <Box data-slot="input-group" className={className}>
       {children}
-    </div>
+    </Box>
   )
 }
 
 interface InputIconProps {
   children: React.ReactNode
-  position: "start" | "end"
+  position: 'start' | 'end'
   className?: string
 }
 
 function InputIcon({ children, position, className }: InputIconProps) {
   return (
-    <span
+    <Box
       data-slot={`input-icon-${position}`}
-      className={cn(
-        "pointer-events-none absolute top-1/2 -translate-y-1/2 text-muted-foreground [&_svg]:size-4",
-        position === "start" && "left-2.5",
-        position === "end" && "right-2.5",
-        className
-      )}
+      component="span"
+      className={className}
+      style={{
+        display: 'inline-flex',
+        alignItems: 'center',
+        pointerEvents: 'none',
+      }}
     >
       {children}
-    </span>
+    </Box>
   )
 }
 
 export { Input, InputGroup, InputIcon }
+export type { InputGroupProps, InputIconProps }