feat(nouser-explorer): integración al stack yahweh themed

Iter 10. nouser-explorer (paralela a nakui-explorer pero para ver
Mónadas via daemon nouser) tenía colors hardcoded idénticos al
patrón previo. Aplico el mismo refactor: theme global instalado,
chrome a slots, widgets compartidos.

- Nuevas deps: yahweh-theme + 3 widgets (banner, card,
  theme-switcher).
- main() instala Theme::install_default.
- render: 4 vars rgb() chrome → theme slots.
- Header: flex_row + theme switcher a la derecha (mismo pattern
  que nakui-explorer).
- error_banner: div hardcoded → banner_themed(Error).
- 2 cards (Engine/Monad): div().flex_col().p().bg().rounded()...
  → card_themed(cx).border_l_4().border_color(accent).
- Accents semánticos (engine cyan, data purple) quedan locales
  como señales de dominio.

Las dos apps explorer del repo ahora comparten paleta themed +
switcher común.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/apps/nouser-explorer/Cargo.toml

@@ -9,6 +9,10 @@ description = "Explorador GPUI de Mónadas: panel que descubre al daemon nouser
 brahman-card = { path = "../../core/brahman-card" }
 brahman-sidecar = { path = "../../shared/brahman-sidecar" }
 nouser-card = { path = "../../modules/nouser/card" }
+yahweh-theme = { path = "../../modules/ui_engine/libs/theme" }
+yahweh-widget-banner = { path = "../../modules/ui_engine/widgets/banner" }
+yahweh-widget-card = { path = "../../modules/ui_engine/widgets/card" }
+yahweh-widget-theme-switcher = { path = "../../modules/ui_engine/widgets/theme-switcher" }
 gpui = { workspace = true }
 
 [[bin]]