feat(juice): button press feedback + fade screen transitions

Adds PressableScale (0.94 squish on tap-down) around the Adventure
FilledButton, Classic OutlinedButton, and each season-map stage node.
Replaces all in-app MaterialPageRoute pushes with a gentle fade+scale
PageRouteBuilder (320ms in, 240ms out) via a new fadeRoute helper.

lib/ui/widgets/fade_route.dart

@@ -0,0 +1,22 @@
+// lib/ui/widgets/fade_route.dart
+import 'package:flutter/material.dart';
+
+/// A gentle fade(+slight scale) page transition for in-app navigation.
+Route<T> fadeRoute<T>(Widget page) {
+  return PageRouteBuilder<T>(
+    transitionDuration: const Duration(milliseconds: 320),
+    reverseTransitionDuration: const Duration(milliseconds: 240),
+    pageBuilder: (_, _, _) => page,
+    transitionsBuilder: (_, animation, _, child) {
+      final curved =
+          CurvedAnimation(parent: animation, curve: Curves.easeOutCubic);
+      return FadeTransition(
+        opacity: curved,
+        child: ScaleTransition(
+          scale: Tween(begin: 0.98, end: 1.0).animate(curved),
+          child: child,
+        ),
+      );
+    },
+  );
+}