feat: nuevos componentes UI — accordion, avatar, breadcrumb, checkbox, command, dropdown, pagination, popover, radio, sheet, select, switch, textarea, toast

Componentes React accesibles basados en Radix UI con soporte de temas via CSS variables. Incluye barrel export en index.ts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/functions/ui/accordion.md

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+---
+name: accordion
+kind: component
+lang: ts
+domain: ui
+version: "1.0.0"
+purity: impure
+signature: "Accordion(props: AccordionProps): JSX.Element"
+description: "Secciones colapsables con animaciones. Base-UI Collapsible primitive. Composable: AccordionItem + AccordionTrigger + AccordionContent."
+tags: [accordion, collapsible, component, ui, interactive, base-ui]
+uses_functions: [cn_ts_core]
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: ["@base-ui/react/collapsible", "lucide-react"]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "frontend/functions/ui/accordion.tsx"
+props:
+  - name: className
+    type: "string"
+    required: false
+    description: "Clases CSS adicionales para el contenedor"
+emits: []
+has_state: false
+framework: react
+variant: []
+---
+
+## Ejemplo
+
+```tsx
+<Accordion>
+  <AccordionItem defaultOpen>
+    <AccordionTrigger>Seccion 1</AccordionTrigger>
+    <AccordionContent>
+      Contenido de la primera seccion.
+    </AccordionContent>
+  </AccordionItem>
+  <AccordionItem>
+    <AccordionTrigger>Seccion 2</AccordionTrigger>
+    <AccordionContent>
+      Contenido de la segunda seccion.
+    </AccordionContent>
+  </AccordionItem>
+</Accordion>
+```
+
+## Notas
+
+Cada AccordionItem es un Collapsible independiente — permite multiples items abiertos simultaneamente. Para exclusividad (solo uno abierto), manejar el estado externamente. El chevron rota 180 grados con [data-open]. Exports: Accordion, AccordionItem, AccordionTrigger, AccordionContent.