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>

crates/apps/lapaloma-demo/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "lapaloma-demo"
+version = { workspace = true }
+edition = { workspace = true }
+license = { workspace = true }
+authors = { workspace = true }
+publish = { workspace = true }
+description = "Lapaloma — demo app: una serie sin(x) sobre ChartViewport rendereada con LapalomaChartElement. Valida la cadena core → render → cartesian → gpui en vivo."
+
+[dependencies]
+gpui = { workspace = true }
+yahweh-launcher = { path = "../../modules/ui_engine/libs/launcher" }
+yahweh-theme = { path = "../../modules/ui_engine/libs/theme" }
+lapaloma-core = { path = "../../modules/ui_engine/libs/lapaloma-core" }
+lapaloma-render = { path = "../../modules/ui_engine/widgets/lapaloma-render", features = ["gpui"] }
+lapaloma-cartesian = { path = "../../modules/ui_engine/widgets/lapaloma-cartesian" }