chore(deps): migrate to Bevy 0.18

- BorderRadius is no longer a Component; moved into Node.border_radius
  field at all 15 spawn sites across 6 plugin files
- Events<T> renamed to Messages<T> in test code (12 files)
- KeyboardEvents SystemParam renamed to KeyboardMessages to match the
  MessageWriter rename done in the 0.17 hop
- WindowResolution::from((f32,f32)) removed; use (u32,u32) tuple in main.rs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/weekly_goals_plugin.rs

@@ -228,7 +228,7 @@ mod tests {
         let base_win_xp = solitaire_data::xp_for_win(60, false);
         assert_eq!(p.total_xp - xp_before, base_win_xp + WEEKLY_GOAL_XP);
 
-        let events = app.world().resource::<Events<WeeklyGoalCompletedEvent>>();
+        let events = app.world().resource::<Messages<WeeklyGoalCompletedEvent>>();
         let mut cursor = events.get_cursor();
         let fired: Vec<_> = cursor.read(events).cloned().collect();
         assert!(fired.iter().any(|e| e.goal_id == "weekly_3_fast"));
@@ -286,7 +286,7 @@ mod tests {
         });
         app.update();
 
-        let events = app.world().resource::<Events<LevelUpEvent>>();
+        let events = app.world().resource::<Messages<LevelUpEvent>>();
         let mut cursor = events.get_cursor();
         let fired: Vec<_> = cursor.read(events).copied().collect();
         assert!(!fired.is_empty(), "LevelUpEvent must fire when weekly bonus pushes past a level threshold");