refactor(engine): audit and rationalize platform cfg gates (closes #49)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

solitaire_engine/src/sync_setup_plugin.rs

@@ -52,6 +52,7 @@ use crate::events::{
     SyncLogoutRequestEvent,
 };
 use crate::font_plugin::FontResource;
+use crate::platform::SHOW_KEYBOARD_ACCELERATORS;
 use crate::settings_plugin::{SettingsPanel, SettingsResource, SettingsScreen, SettingsStoragePath};
 use crate::resources::TokioRuntimeResource;
 use crate::sync_plugin::SyncProviderResource;
@@ -723,13 +724,14 @@ fn spawn_sync_setup_modal(commands: &mut Commands, font_res: Option<&FontResourc
                 ));
             });
 
-            // Tab hint — desktop only; no Tab key on Android.
-            #[cfg(not(target_os = "android"))]
-            body.spawn((
-                Text::new("Tab  =  next field"),
-                make_font(font_res, TYPE_CAPTION),
-                TextColor(TEXT_DISABLED),
-            ));
+            // Tab hint — desktop only; no Tab key on touch-first Android builds.
+            if SHOW_KEYBOARD_ACCELERATORS {
+                body.spawn((
+                    Text::new("Tab  =  next field"),
+                    make_font(font_res, TYPE_CAPTION),
+                    TextColor(TEXT_DISABLED),
+                ));
+            }
         });
 
         // Action row.