fix(components): add unoptimized image prop, overflow containment, and accessibility

Add unoptimized prop to image preview to support blob URLs, contain
overflow on preview container, replace div with semantic section
element in DragDropContainer with aria-label, and import shared
image constants.

src/components/drag-drop-container.tsx

@@ -1,7 +1,6 @@
-import { ReactNode } from "react";
+import type { ReactNode } from "react";
 import { toast } from "sonner";
-
-const IMAGE_EXTENSIONS = [".png", ".jpg", ".jpeg", ".webp"];
+import { IMAGE_EXTENSIONS } from "@/lib/constants";
 
 const getFileType = (file: File): "ics" | "image" | null => {
 	const name = file.name.toLowerCase();
@@ -53,7 +52,8 @@ export const DragDropContainer = ({
 	};
 
 	return (
-		<div
+		<section
+			aria-label="Drag and drop file import area"
 			onDragOver={handleDragOver}
 			onDragLeave={handleDragLeave}
 			onDrop={handleDrop}
@@ -67,6 +67,6 @@ export const DragDropContainer = ({
 					Drag & Drop *.ics or an event screenshot here
 				</div>
 			</div>
-		</div>
+		</section>
 	);
 };