🐛 fix Nisse outline only shown when actually occluded

Silhouette now hidden by default and toggled on per frame only when
isOccluded() detects a tree, rock or building 1–3 tiles below the Nisse.
Adds WorldSystem.hasResourceAt() for O(1) tile lookup. Outline colour
changed to light blue (0xaaddff) at scale 1.1.

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

src/systems/WorldSystem.ts

@@ -172,6 +172,16 @@ export class WorldSystem {
     this.resourceTiles.delete(tileY * WORLD_TILES + tileX)
   }
 
+  /**
+   * Returns true if a resource (tree or rock) occupies the given tile.
+   * Uses the O(1) resourceTiles index.
+   * @param tileX - Tile column
+   * @param tileY - Tile row
+   */
+  hasResourceAt(tileX: number, tileY: number): boolean {
+    return this.resourceTiles.has(tileY * WORLD_TILES + tileX)
+  }
+
   /**
    * Converts world pixel coordinates to tile coordinates.
    * @param worldX - World X in pixels