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/popover.md

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+---
+name: popover
+kind: component
+lang: ts
+domain: ui
+version: "1.0.0"
+purity: impure
+signature: "Popover(props: PopoverProps): JSX.Element"
+description: "Contenido flotante posicionado accesible con animaciones. Base-UI Popover primitive."
+tags: [popover, component, ui, interactive, overlay, base-ui]
+uses_functions: [cn_ts_core]
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: ["@base-ui/react/popover"]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "frontend/functions/ui/popover.tsx"
+props:
+  - name: open
+    type: "boolean"
+    required: false
+    description: "Estado controlado de apertura"
+  - name: defaultOpen
+    type: "boolean"
+    required: false
+    description: "Estado inicial de apertura (no controlado)"
+  - name: onOpenChange
+    type: "(open: boolean) => void"
+    required: false
+    description: "Callback cuando cambia el estado de apertura"
+  - name: sideOffset
+    type: "number"
+    required: false
+    description: "Distancia en px entre trigger y popover (default: 4)"
+emits: [onOpenChange]
+has_state: false
+framework: react
+variant: []
+---
+
+## Ejemplo
+
+```tsx
+<Popover>
+  <PopoverTrigger asChild>
+    <Button variant="outline">Abrir</Button>
+  </PopoverTrigger>
+  <PopoverContent>
+    <PopoverHeader>
+      <PopoverTitle>Configuracion</PopoverTitle>
+      <PopoverDescription>Ajusta tus preferencias.</PopoverDescription>
+    </PopoverHeader>
+    <div className="mt-4">
+      {/* contenido */}
+    </div>
+  </PopoverContent>
+</Popover>
+```
+
+## Notas
+
+Compuesto de: Popover (root), PopoverTrigger, PopoverContent (positioner + popup), PopoverClose, PopoverHeader, PopoverTitle, PopoverDescription. El posicionamiento automatico lo maneja Base-UI. Animaciones con data-open/data-closed.