fix(alarma-sonando): pulsing halo, hero-time metrics, art size, snooze icon

Tier 4 visual fidelity, audit 9.1/9.5/9.6/9.8 (t4 lines 411-428):

- 9.1: new _HaloPulsante renders the prototype's 420px amber radial
  gradient behind the hero content. Deliberately BOUNDED (one
  grow-and-settle cycle), not the prototype's literal `infinite` CSS
  animation: this screen's protected dismiss-guard test calls
  pumpAndSettle() after every mount/interaction, and a genuinely
  infinite AnimationController.repeat() would hang it forever with no
  way to fix it. Skips its Animate wrapper under reduced motion, same
  as every other entry animation in this app.
- 9.5: the hero time gets a local letterSpacing/height override
  (-4/0.95) instead of the shared heroTime token's -2.0/1.0 — the
  alarm editor's hour block is the token's other consumer and still
  wants height:1, so the shared style is untouched.
- 9.6: ringing-screen art grows from 168/radiusLg(30) to 180/36 (t4
  line 421), a local constant like the existing stop-button radius.
- 9.8: the POSPONER eyebrow regains its 19px warmCoral snooze icon.

All 5 protected files (including the dismiss-guard test) remain
empty-diff against main.

test/pantallas/pantalla_alarma_sonando_scaffold_test.dart

@@ -146,7 +146,8 @@ void main() {
 
   group('WU11 — restyle a pantalla completa', () {
     testWidgets(
-      'el tiempo gigante usa PluriWaveTypography.heroTime envuelto en '
+      'el tiempo gigante usa PluriWaveTypography.heroTime (con un ajuste '
+      'local de letter-spacing/height, audit 9.5) envuelto en '
       'FittedBox(scaleDown)',
       (tester) async {
         await _montarPantalla(tester);
@@ -155,7 +156,22 @@ void main() {
         expect(heroFinder, findsOneWidget);
         final texto = tester.widget<Text>(heroFinder);
         final contexto = tester.element(heroFinder);
-        expect(texto.style, contexto.pluriType.heroTime);
+        final base = contexto.pluriType.heroTime;
+        // Audit 9.5 (t4 line 417): the prototype wants 88px/w800/ls-4/lh.95
+        // on THIS screen only. heroTime itself must stay ls-2.0/height 1.0
+        // — EditorHoraInline (the alarm editor's hour block) is the other
+        // consumer and wants height:1 (t4 line 379) — so this is a LOCAL
+        // copyWith override, not a change to the shared token.
+        expect(texto.style?.fontSize, base.fontSize);
+        expect(texto.style?.fontWeight, base.fontWeight);
+        expect(texto.style?.letterSpacing, -4);
+        expect(texto.style?.height, 0.95);
+        expect(
+          base.letterSpacing,
+          -2.0,
+          reason: 'the shared token is unchanged',
+        );
+        expect(base.height, 1.0, reason: 'the shared token is unchanged');
         expect(
           find.ancestor(of: heroFinder, matching: find.byType(FittedBox)),
           findsOneWidget,