fix(nav,favoritos): unclip the overflow menu and smooth the tab transition

Two user-reported bugs from on-device testing.

The favourites overflow menu carried `constraints: tightFor(38x42)`,
which sizes the POPUP rather than the button -- every item was clipped to
its first letter, so users saw "M" and "E" instead of the labels. The
existing test passed throughout because find.text matches a Text widget
whether or not it is visually clipped; the new guard measures the laid-out
width instead.

The bottom bar's ink splash had no shape, painting a hard square over the
icon, and the active tab's lift, dim, icon size and label all changed
instantly while the balloon slid -- the balloon glided and its contents
teleported. All four now share the balloon's duration and curve.

test/widgets/pluri_bottom_navigation_test.dart

@@ -96,13 +96,17 @@ void main() {
     );
     expect(inactiveIcon.color, isNull);
 
-    final dimmed = tester.widget<Opacity>(
+    // AnimatedOpacity, not a plain Opacity: the dim now transitions with the
+    // balloon instead of snapping. Users reported the bar's contents
+    // teleporting while the balloon slid — the lift, dim, icon size and
+    // label all animate together now.
+    final dimmed = tester.widget<AnimatedOpacity>(
       find.ancestor(
         of: find.descendant(
           of: find.byKey(PluriBottomNavigation.itemKey(1)),
           matching: find.byType(PluriIcon),
         ),
-        matching: find.byType(Opacity),
+        matching: find.byType(AnimatedOpacity),
       ),
     );
     expect(dimmed.opacity, closeTo(0.46, 0.001));