feat(yahweh-widget-card): container card-shape compartido para timeline entries

Iter 3 de integración nakui↔yahweh. El card visual pattern (padding
consistente + rounded + flex_col + gap) que vivía duplicado en cada
timeline entry de nakui-explorer ahora es un widget yahweh reusable.

crates/modules/ui_engine/widgets/card/:
- pub fn card() -> Div: flex_col + px(12) + py(8) + mb(4) +
  rounded(4) + gap(2). Sin colores (caller decide via builder).
- 1 test smoke.

nakui-explorer:
- Los 2 timeline entry patterns (Seed/Morphism) pasan de ~7
  calls a ~3, intención "card with accent" emerge del nombre.

Tests stack: 111 → 112. App-agnostic — el widget no impone paleta,
permite themes diversos.

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

crates/apps/nakui-explorer/src/main.rs

@@ -32,6 +32,7 @@ use gpui::{
 use nakui_core::event_log::{EventLog, LogEntry};
 use yahweh_meta_runtime::{preview_value, short_hash, short_uuid};
 use yahweh_widget_banner::{banner, Banner};
+use yahweh_widget_card::card;
 
 const REFRESH_INTERVAL: Duration = Duration::from_secs(2);
 
@@ -224,17 +225,10 @@ impl Render for Explorer {
                         .as_ref()
                         .map(|h| format!("schema={}", short_hash(h)))
                         .unwrap_or_else(|| "schema=(legacy)".into());
-                    div()
-                        .flex()
-                        .flex_col()
-                        .px(px(12.))
-                        .py(px(8.))
-                        .mb(px(4.))
+                    card()
                         .bg(card_bg)
-                        .rounded(px(4.))
                         .border_l_4()
                         .border_color(accent_seed)
-                        .gap(px(2.))
                         .child(
                             div()
                                 .flex()
@@ -297,17 +291,10 @@ impl Render for Explorer {
                         .as_ref()
                         .map(|h| format!("schema={}", short_hash(h)))
                         .unwrap_or_else(|| "schema=(legacy)".into());
-                    div()
-                        .flex()
-                        .flex_col()
-                        .px(px(12.))
-                        .py(px(8.))
-                        .mb(px(4.))
+                    card()
                         .bg(card_bg)
-                        .rounded(px(4.))
                         .border_l_4()
                         .border_color(accent_morphism)
-                        .gap(px(2.))
                         .child(
                             div()
                                 .flex()