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/search_bar.md

@@ -8,12 +8,12 @@ purity: impure
 signature: "SearchBar(props: SearchBarProps): JSX.Element"
 description: "Search input with debounce, search icon, and clear button"
 tags: [component, ui, search, input, debounce]
-uses_functions: [cn_ts_core]
+uses_functions: []
 uses_types: []
 returns: []
 returns_optional: false
 error_type: ""
-imports: ["lucide-react"]
+imports: ["@mantine/core", "@tabler/icons-react"]
 params:
   - name: onSearch
     desc: "Callback que se ejecuta con la query debounceada"