fix(alarma-sonando): make the snooze block's vertical gaps uniform

Issue 3 (feedback-pruebas): t4:427 wraps the POSPONER eyebrow, the
snooze tiles and the Stop button in a single flex column with a
uniform gap:12 -- this screen carried a 10/14 pair instead, matching
neither the prototype nor each other.

The dismiss-guard test (protected, untouched) only asserts behaviour
via find.text/find.byType, so this pure value change is safe against
it -- re-verified empty diff after this commit.

lib/pantallas/pantalla_alarma_sonando.dart

@@ -339,14 +339,18 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
                       ],
                     ),
                   ),
-                  const SizedBox(height: 10),
+                  // Issue 3 (feedback-pruebas): t4:427 wraps POSPONER's
+                  // eyebrow, the snooze tiles and Stop in a `gap:12` flex
+                  // column -- the same 12 on both sides, not the 10/14 pair
+                  // this used to carry.
+                  const SizedBox(height: 12),
                   _FilaSnoozeFija(
                     alarma: alarma,
                     l10n: l10n,
                     tokens: tokens,
                     onPosponer: _posponer,
                   ),
-                  const SizedBox(height: 14),
+                  const SizedBox(height: 12),
                   SizedBox(
                     width: double.infinity,
                     child: FilledButton.icon(

test/pantallas/pantalla_alarma_sonando_tier5_test.dart

@@ -159,4 +159,49 @@ void main() {
       await tester.pumpAndSettle();
     },
   );
+
+  testWidgets(
+    'Issue 3 (feedback-pruebas): the gap above the snooze tiles matches the '
+    'gap below them (t4:427 draws a uniform gap:12 flex column) -- the '
+    'previous 10/14 pair matched neither the prototype nor each other',
+    (tester) async {
+      await _montarPantalla(tester);
+      final l10n = AppLocalizations.of(
+        tester.element(find.byType(PantallaAlarmaSonando)),
+      );
+
+      final eyebrowBottom =
+          tester
+              .getBottomLeft(
+                find
+                    .ancestor(
+                      of: find.byIcon(Icons.snooze_rounded),
+                      matching: find.byType(Row),
+                    )
+                    .first,
+              )
+              .dy;
+      final tileDestacado = find.ancestor(
+        of: find.text(l10n.alarmSnoozeOptionLabel(10)),
+        matching: find.byType(FilledButton),
+      );
+      final tilesTop = tester.getTopLeft(tileDestacado).dy;
+      final tilesBottom = tester.getBottomLeft(tileDestacado).dy;
+      final stopButtonTop =
+          tester
+              .getTopLeft(find.byKey(const ValueKey('ringing-stop-button')))
+              .dy;
+
+      expect(
+        tilesTop - eyebrowBottom,
+        12,
+        reason: 't4:427: gap:12 above the snooze tiles',
+      );
+      expect(
+        stopButtonTop - tilesBottom,
+        12,
+        reason: 't4:427: gap:12 below the snooze tiles, same as above',
+      );
+    },
+  );
 }