feat: add lightbox for viewing forest and reward images fullscreen

- Click any forest element or reward image to see it large
- Smooth zoom-in animation, click anywhere to close
- Hover effect on clickable images
- Works on both forest grid and reward screen

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main.ts

@@ -64,4 +64,27 @@ document.addEventListener("DOMContentLoaded", async () => {
 	};
 	document.addEventListener("click", initAudioOnce);
 	document.addEventListener("keydown", initAudioOnce);
+
+	// Lightbox: click on forest/reward images to view fullscreen
+	const lightbox = document.getElementById("image-lightbox")!;
+	const lightboxImg = document.getElementById("lightbox-img") as HTMLImageElement;
+
+	document.addEventListener("click", (e) => {
+		const target = e.target as HTMLElement;
+		// Open lightbox when clicking forest element or reward image
+		if (
+			(target.tagName === "IMG" && target.closest(".forest__element")) ||
+			(target.tagName === "IMG" && target.closest(".reward__image-area"))
+		) {
+			lightboxImg.src = (target as HTMLImageElement).src;
+			lightboxImg.alt = (target as HTMLImageElement).alt;
+			lightbox.style.display = "flex";
+		}
+	});
+
+	// Close lightbox on click
+	lightbox.addEventListener("click", () => {
+		lightbox.style.display = "none";
+		lightboxImg.src = "";
+	});
 });