Fix linter/transpiler errors, formatting

models/article.ts

@@ -28,7 +28,7 @@ export default class Article {
     return tag ? tag[1] : "Untitled";
   }
 
-  get image(): string {
+  get image(): string | undefined {
     const tag = this.event.tags.find((t) => t[0] === "image");
     return tag ? tag[1] : undefined;
   }