brand: de-cake new-ui asset filenames + drop unused cake art

Rename the new-ui assets (source in res/pictures + compiled .svg.vec in
assets/new-ui) and their 3 code refs. Content was already Hash Bags; only the
filenames were cake:
- cake_squircle_icon      -> hash_squircle_icon   (About page)
- cakewallet-wordmark(.light) -> hash-wordmark(.light) (receive QR)
- cake-setting            -> hash-setting          (settings)

Remove unused cake assets (0 refs): by-cakelabs, cakelabs-icon, new-ui cupcake
duplicate, cake_icon.png, cake_wordmark.png. (assets/images/cupcake* kept — that
is Cake's Cupcake hardware-signer device name, a real integration, not branding.)

lib/new-ui/pages/about_page.dart

@@ -70,7 +70,7 @@ class _AboutPageState extends State<AboutPage> {
                     GestureDetector(
                       onTap: _easterEgg,
                       child: HashImageWidget(
-                        imageUrl: "assets/new-ui/cake_squircle_icon.svg",
+                        imageUrl: "assets/new-ui/hash_squircle_icon.svg",
                         width: 128,
                         height: 128,
                       ),

lib/new-ui/pages/settings_page.dart

@@ -62,7 +62,7 @@ class SettingsSectionData {
   ]);
 
   static SettingsSectionData appSettings =
-      SettingsSectionData(S.current.app_settings, "assets/new-ui/cake-setting.svg", [
+      SettingsSectionData(S.current.app_settings, "assets/new-ui/hash-setting.svg", [
     SettingsListItem("assets/new-ui/settings_row_icons/connections.svg", S.current.connections, Routes.connectionSync),
     // SettingsListItem("assets/new-ui/settings_row_icons/defaults.svg", "Defaults", ""),
     SettingsListItem("assets/new-ui/settings_row_icons/display.svg", S.current.display, Routes.displaySettingsPage),

lib/new-ui/widgets/receive_page/receive_qr_code.dart

@@ -44,8 +44,8 @@ class ReceiveQrCode extends StatelessWidget {
               opacity: largeQrMode ? 1 : 0,
               child: HashImageWidget(imageUrl:
                 isLightMode
-                    ? "assets/new-ui/cakewallet-wordmark-light.svg"
-                    : "assets/new-ui/cakewallet-wordmark.svg",
+                    ? "assets/new-ui/hash-wordmark-light.svg"
+                    : "assets/new-ui/hash-wordmark.svg",
                 height: 45,
               )),
         ),