Tint a collider's area only while the collider itself is selected

A collider filled its area with a faint green in the scene view all the
time. It lay over every sprite a collider sits on and made the art look
washed out. The outline alone shows where a collider is. The area only
matters while one works on that collider.

- drawItem takes a selected flag. Only a selected collider is filled,
  every other one is drawn as its outline.
- The fill is stronger than before, alpha 0.3 instead of 0.12, so the
  selected area is easy to see. The value is COLLIDER_FILL_ALPHA in
  src/viewport/symbols.ts.
- The scene view says what is selected through isSelected. The game
  view keeps the default and never fills.
- Only the collider object itself counts. Selecting its body leaves
  the area unfilled.

Tests:
- 2 new unit tests in tests/viewport/collider-color.test.ts read the
  Pixi instructions: outline only when not selected, fill at 0.3 and
  outline when selected.
- Counter check: with the fill drawn regardless of selection the
  outline-only test fails. The original is back per cmp.
- ./check.sh: 158 files, 2334 tests, CHECK EXIT 0.
- e2e 1-17,28-30: no FAIL. e2e 39-43: ALL PASSED, 145 checks.
  A first run left out 39, which 40 builds on, and failed 8 checks
  in 40 for the missing tile only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/viewport/SceneViewport.ts

@@ -363,6 +363,11 @@ export class SceneViewport extends FreeViewport {
     return this.corners.info();
   }
 
+  protected override isSelected(objectId: string): boolean {
+    const s = this.state.selection;
+    return s?.kind === 'object' && s.objectIds.includes(objectId);
+  }
+
   /**
    * Pixi only says which hit area was pressed; what is really under the pointer is worked out
    * here, in the order it is drawn (#203): a tilemap's grid is empty where it has no tile, and a

src/editor/viewport/WorldViewport.ts

@@ -137,6 +137,11 @@ export abstract class WorldViewport extends Widget {
 
   protected onItemPointerDown(_objectId: string, _e: FederatedPointerEvent): void {}
 
+  /** Whether the object itself is selected – a selected collider shows its area filled. */
+  protected isSelected(_objectId: string): boolean {
+    return false;
+  }
+
   /** Screen-space drawing that follows the camera, redrawn after a full redraw and after a pan. */
   protected drawOnScreen(_items: DrawItem[], _view: View): void {}
 
@@ -317,7 +322,13 @@ export abstract class WorldViewport extends Widget {
       this.syncTilemap(item, onScreen);
       if (!onScreen) continue;
       this.visibleCount++;
-      drawItem(node, item, size, view.scale * scaleOf(placementOf(item.type, item.m)));
+      drawItem(
+        node,
+        item,
+        size,
+        view.scale * scaleOf(placementOf(item.type, item.m)),
+        this.isSelected(item.id),
+      );
     }
     this.afterItems(items, view);
     this.drawOnScreen(items, view);