feat: mejoras componentes UI — card variants, kpi_card slots, sparkline colors, bar_chart horizontal radius

- card: variantes default/borderless/ghost con ring condicional
- kpi_card: props unit, action, chart y delta con label/suffix personalizable
- sparkline: prop colors para colores por barra en variant bar
- bar_chart: radius condicional según orientación horizontal/vertical

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

frontend/functions/ui/card.md

@@ -3,11 +3,11 @@ name: card
 kind: component
 lang: ts
 domain: ui
-version: "1.0.0"
+version: "1.1.0"
 purity: impure
-signature: "Card(props: { size?: 'default' | 'sm'; className?: string; children: ReactNode }): JSX.Element"
-description: "Contenedor card con header, title, description, action, content y footer. Sistema de slots composable."
-tags: [card, container, layout, component, ui]
+signature: "Card(props: { size?: 'default' | 'sm'; variant?: 'default' | 'borderless' | 'ghost'; className?: string; children: ReactNode }): JSX.Element"
+description: "Contenedor card con header, title, description, action, content y footer. Sistema de slots composable. Variantes default, borderless y ghost para dashboards dark."
+tags: [card, container, layout, component, ui, dashboard, dark]
 uses_functions: [cn_typescript_core]
 uses_types: []
 returns: []
@@ -23,6 +23,10 @@ props:
     type: "'default' | 'sm'"
     required: false
     description: "Tamaño del card"
+  - name: variant
+    type: "'default' | 'borderless' | 'ghost'"
+    required: false
+    description: "Variante visual. borderless quita borde/shadow, ghost además hace bg transparente"
   - name: className
     type: "string"
     required: false
@@ -30,7 +34,7 @@ props:
 emits: []
 has_state: false
 framework: react
-variant: [default, sm]
+variant: [default, sm, borderless, ghost]
 source_repo: "https://gitea-dgg044oo04woo4ggcsws4gk0.organic-machine.com/Bl4cksmith/Frontend_Library"
 source_license: "MIT"
 source_file: "frontend/src/components/ui/card.tsx"
@@ -47,8 +51,20 @@ source_file: "frontend/src/components/ui/card.tsx"
   <CardContent>Contenido</CardContent>
   <CardFooter>Footer</CardFooter>
 </Card>
+
+{/* Dashboard dark — sin bordes */}
+<Card variant="borderless">
+  <CardContent>Widget sin marco</CardContent>
+</Card>
+
+{/* Completamente transparente */}
+<Card variant="ghost">
+  <CardContent>Sin fondo ni borde</CardContent>
+</Card>
 ```
 
 ## Notas
 
 Sistema de slots via data-slot attributes. Card detecta automáticamente la presencia de CardFooter y ajusta el padding. Exporta 7 subcomponentes composables.
+
+Las variantes `borderless` y `ghost` eliminan el `ring-1` del borde por defecto. `ghost` además hace el fondo transparente. Alternativa con CSS global: `[data-slot="card"] { --tw-ring-opacity: 0; }` o `[data-variant="borderless"] { ring: 0 }` via `data-variant` attribute expuesto.