♻️ (bootsier): Reorganiza en capas token/class/bs

Sustituye `attrs/` y `classes/` por tres capas diferenciadas:
- `token/`: primitivas CSS (BreakPoint, Color, ScaleSize, etc.).
- `class/`: tipos compuestos (Border, Background, Margin, etc.).
- `bs/*/props.rs`: props tipadas para cada componente de Bootstrap.

El patrón de construcción es `suffix()` -> `push_to()` -> `to_class()`.
`push_to()` es `pub` en `class/` y `bs/*/props.rs` para que los temas
derivados puedan acceder a los mismos mecanismos de construcción.

extensions/pagetop-bootsier/src/theme/bs/icon.rs

@@ -0,0 +1,130 @@
+use crate::theme::*;
+
+const DEFAULT_VIEWBOX: &str = "0 0 16 16";
+
+#[derive(AutoDefault, Clone)]
+pub enum IconKind {
+    #[default]
+    None,
+    Font(FontSize),
+    Svg {
+        shapes: Markup,
+        viewbox: AttrValue,
+    },
+}
+
+#[derive(AutoDefault, Clone, Debug, Getters)]
+pub struct Icon {
+    /// Devuelve los atributos HTML y clases CSS del componente.
+    props: Props,
+    icon_kind: IconKind,
+    aria_label: AttrL10n,
+}
+
+impl Component for Icon {
+    fn new() -> Self {
+        Self::default()
+    }
+
+    fn id(&self) -> Option<String> {
+        self.props.get_id()
+    }
+
+    fn setup(&mut self, _cx: &Context) {
+        if !matches!(self.icon_kind(), IconKind::None) {
+            self.alter_prop(PropsOp::prepend_classes("icon"));
+        }
+        if let IconKind::Font(font_size) = self.icon_kind() {
+            self.alter_prop(PropsOp::add_classes(font_size.as_str()));
+        }
+    }
+
+    fn prepare(&self, cx: &mut Context) -> Result<Markup, ComponentError> {
+        Ok(match self.icon_kind() {
+            IconKind::None => html! {},
+            IconKind::Font(_) => {
+                let aria_label = self.aria_label().lookup(cx);
+                let has_label = aria_label.is_some();
+                html! {
+                    i
+                        (self.props())
+                        role=[has_label.then_some("img")]
+                        aria-label=[aria_label]
+                        aria-hidden=[(!has_label).then_some("true")]
+                    {}
+                }
+            }
+            IconKind::Svg { shapes, viewbox } => {
+                let aria_label = self.aria_label().lookup(cx);
+                let has_label = aria_label.is_some();
+                let viewbox = viewbox.get().unwrap_or_else(|| DEFAULT_VIEWBOX.to_string());
+                html! {
+                    svg
+                        xmlns="http://www.w3.org/2000/svg"
+                        viewBox=(viewbox)
+                        fill="currentColor"
+                        focusable="false"
+                        (self.props())
+                        role=[has_label.then_some("img")]
+                        aria-label=[aria_label]
+                        aria-hidden=[(!has_label).then_some("true")]
+                    {
+                        (shapes)
+                    }
+                }
+            }
+        })
+    }
+}
+
+impl Icon {
+    pub fn font() -> Self {
+        Self::default().with_icon_kind(IconKind::Font(FontSize::default()))
+    }
+
+    pub fn font_sized(font_size: FontSize) -> Self {
+        Self::default().with_icon_kind(IconKind::Font(font_size))
+    }
+
+    pub fn svg(shapes: Markup) -> Self {
+        Self::default().with_icon_kind(IconKind::Svg {
+            shapes,
+            viewbox: AttrValue::default(),
+        })
+    }
+
+    pub fn svg_with_viewbox(shapes: Markup, viewbox: impl AsRef<str>) -> Self {
+        Self::default().with_icon_kind(IconKind::Svg {
+            shapes,
+            viewbox: AttrValue::new(viewbox),
+        })
+    }
+
+    // **< Icon BUILDER >***************************************************************************
+
+    /// Establece el identificador único del componente; igual a `with_prop(PropsOp::set_id(id))`.
+    #[builder_fn]
+    pub fn with_id(mut self, id: impl Into<CowStr>) -> Self {
+        self.props.alter_id(id);
+        self
+    }
+
+    /// Modifica identificador, clases CSS o atributos HTML del componente.
+    #[builder_fn]
+    pub fn with_prop(mut self, op: PropsOp) -> Self {
+        self.props.alter_prop(op);
+        self
+    }
+
+    #[builder_fn]
+    pub fn with_icon_kind(mut self, icon_kind: IconKind) -> Self {
+        self.icon_kind = icon_kind;
+        self
+    }
+
+    #[builder_fn]
+    pub fn with_aria_label(mut self, label: L10n) -> Self {
+        self.aria_label.alter_value(label);
+        self
+    }
+}