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/auto_complete_plugin.rs

@@ -190,7 +190,7 @@ mod tests {
         app.update(); // detect runs, sets active
         app.update(); // drive fires the move
 
-        let events = app.world().resource::<Events<MoveRequestEvent>>();
+        let events = app.world().resource::<Messages<MoveRequestEvent>>();
         let mut cursor = events.get_cursor();
         let fired: Vec<_> = cursor.read(events).collect();
         // At least one MoveRequestEvent should have been fired.