feat(ui,learn,todo,train,meditate): a wave in the app's colour over the navigation bar

The developer's choice of 7 Nov 2026 (the mockup's variant E): a tap on
another destination sends a radial glow in the app's colour over the bar
from that destination's centre, solid to 35 % of its radius and gone at
70 %, growing to cover the bar (cubic(.2, .7, .2, 1)) while it fades from
half its strength in dark mode and a third in light, over 1.2 s, behind
the destinations and clipped to the bar. None for the destination already
chosen, none with animations off, and none for a tab changed without a
tap (a link, back): the wave answers the finger. The destination chosen
takes the app's colour, its indicator tinted 22 % with it, without
Material's ripple or the indicator growing; the bar's top corners are
rounded, 20 dp, the screen showing through them.

Each app gives the frame its colour (NavigationFrame's accent, from
PaletteColor): Learn's purple, its icon's last colour, Todo's strawberry,
Train's carrot and Meditate's fern, their screens' wash.

For trying it on a phone, a debug build's Settings has a section
Navigation bar (debug), halkyon_ui's NavigationBarDebugSection, switching
live, in memory alone: the variant (A Material only, C the wave with
Material's fill, E without it, F without the indicator too), the wave's
time (0.7 to 2 s) and the corners (0 to 28 dp). Release builds never read
it and show shippingNavigationBarStyle, the debug section's start: to
remove it, delete the section from the four Settings screens and
debugNavigationBarStyle, and let effectiveNavigationBarStyle return the
shipping style.

Whats-New: Tapping a tab sends a soft wave in the app's colour across the navigation bar, now with rounded corners.
Whats-New-De: Ein Tipp auf einen Tab schickt eine sanfte Welle in der Farbe der App über die Navigationsleiste, jetzt mit abgerundeten Ecken.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_ui/test/widget/navigation_frame_test.dart

@@ -36,6 +36,7 @@ void main() {
         NavigationFrame(
           appName: 'Halkyon Test',
           icon: icon,
+          accent: const Color(0xFFEC3E7C),
           selectedIndex: selected,
           onSelected: chosen.add,
           destinations: const [
@@ -97,8 +98,14 @@ void main() {
       tester.getRect(bar),
       const Rect.fromLTRB(0, 800 - 64 - 24, 400, 800),
     );
-    expect(tester.widget<NavigationBar>(bar).backgroundColor, isNull);
-    expect(tester.widget<NavigationBar>(bar).elevation, isNull);
+    final colour = find.descendant(
+      of: find.byKey(FlushNavigationBar.barKey),
+      matching: find.byType(ColoredBox),
+    );
+    expect(
+      tester.widget<ColoredBox>(colour.first).color,
+      Theme.of(tester.element(bar)).colorScheme.surfaceContainer,
+    );
   });
 
   testWidgets('right above the bar, a fade into the background of the screen '
@@ -115,6 +122,7 @@ void main() {
         NavigationFrame(
           appName: 'Halkyon Test',
           icon: icon,
+          accent: const Color(0xFFEC3E7C),
           selectedIndex: 0,
           onSelected: (_) {},
           destinations: const [
@@ -162,6 +170,7 @@ void main() {
           NavigationFrame(
             appName: 'Halkyon Test',
             icon: icon,
+            accent: const Color(0xFFEC3E7C),
             selectedIndex: 0,
             onSelected: (_) {},
             destinations: const [
@@ -198,6 +207,7 @@ void main() {
         NavigationFrame(
           appName: 'Halkyon Test',
           icon: icon,
+          accent: const Color(0xFFEC3E7C),
           selectedIndex: 0,
           onSelected: (_) {},
           destinations: const [
@@ -329,6 +339,7 @@ void main() {
         NavigationFrame(
           appName: 'Halkyon Test',
           icon: icon,
+          accent: const Color(0xFFEC3E7C),
           selectedIndex: 0,
           onSelected: (_) {},
           hidesNavigationBar: true,
@@ -356,6 +367,7 @@ void main() {
           NavigationFrame(
             appName: 'Halkyon Test',
             icon: icon,
+            accent: const Color(0xFFEC3E7C),
             selectedIndex: 0,
             onSelected: (_) {},
             status: const Text('Recording'),
@@ -391,6 +403,7 @@ void main() {
       NavigationFrame(
         appName: 'Halkyon Test',
         icon: icon,
+        accent: const Color(0xFFEC3E7C),
         selectedIndex: 0,
         onSelected: (_) {},
         destinations: const [