feat(lapaloma): backend GPUI + LapalomaChartElement + app demo

Cadena end-to-end DataBuffer → LineSeries → Canvas → gpui::Window
funcionando. cargo run -p lapaloma-demo abre una ventana con sin(x)
sobre 1024 muestras y una sola paint_path por frame.

- lapaloma-render: feature `gpui` opcional. WindowCanvas adapter
  traduce el trait Canvas a paint_quad/paint_path de gpui 0.2.
  Conversión RGB→HSL para integrar con el sistema de colores Hsla
  del resto del codebase yahweh. 3 tests de conversión.
- lapaloma-cartesian: feature `gpui` (default). element::LapalomaChartElement
  con impl Element + IntoElement. Arma WindowCanvas en paint() y
  delega a LineSeries — un solo paint_path por chart.
- crates/apps/lapaloma-demo registrado en workspace.

Limitaciones conocidas v0.1: clip stack, triangle strips y draw_text
no implementados (los necesitan phosphor / Sankey / axes; se
agregan en sus fases).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -5393,6 +5393,18 @@ dependencies = [
 name = "lapaloma-core"
 version = "0.1.0"
 
+[[package]]
+name = "lapaloma-demo"
+version = "0.1.0"
+dependencies = [
+ "gpui",
+ "lapaloma-cartesian",
+ "lapaloma-core",
+ "lapaloma-render",
+ "yahweh-launcher",
+ "yahweh-theme",
+]
+
 [[package]]
 name = "lapaloma-export"
 version = "0.1.0"
@@ -5461,6 +5473,7 @@ dependencies = [
 name = "lapaloma-render"
 version = "0.1.0"
 dependencies = [
+ "gpui",
  "lapaloma-core",
 ]