feat(yahweh): theme integration en banner + card + nakui-explorer consume themed

Iter 4 de integración nakui↔yahweh. Los widgets banner y card
ofrecen variants _themed(cx, ...) que leen Theme::global(cx).
Versiones sin theme preservadas para apps sin theme global.

yahweh-widget-card:
- Nueva dep yahweh-theme.
- pub fn card_themed(cx: &App) -> Div: card() + bg(theme.bg_panel).

yahweh-widget-banner:
- Nueva dep yahweh-theme.
- pub fn banner_themed(cx, kind, msg) -> Div: deriva (bg, fg) según
  kind + theme.is_dark. Info usa accent del theme; Success/Warning/
  Error usan hue fijo (verde/amber/rojo) + lightness flippeada.
- pub fn themed_colors(kind, theme) -> (Background, Hsla) helper.
- 3 tests nuevos del derivation.

nakui-explorer:
- Nueva dep yahweh-theme.
- main() instala Theme::install_default antes de open_window.
- render: 5 vars rgb() locales → theme slots (bg_app/fg_text/etc).
- card() → card_themed(cx). banner() → banner_themed(cx).
- Accents semánticos del log (seed azul, morphism verde) quedan
  locales: son señales del dominio, no chrome.

Tests: 112 → 115 (+3). Stack intacto.

Beneficio: cambiar de Theme refleja en nakui-explorer automático.
Próximo candidato: migrar MetaApp (paleta hardcoded de 6 colors).

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

Cargo.lock

@@ -6460,6 +6460,7 @@ dependencies = [
  "tempfile",
  "uuid",
  "yahweh-meta-runtime",
+ "yahweh-theme",
  "yahweh-widget-banner",
  "yahweh-widget-card",
 ]
@@ -13005,6 +13006,7 @@ name = "yahweh-widget-banner"
 version = "0.1.0"
 dependencies = [
  "gpui",
+ "yahweh-theme",
 ]
 
 [[package]]
@@ -13012,6 +13014,7 @@ name = "yahweh-widget-card"
 version = "0.1.0"
 dependencies = [
  "gpui",
+ "yahweh-theme",
 ]
 
 [[package]]