refactor: moved components to separate modules

`content.ts` is now half less than the size, exported functions can be unit tested

src/content/utils/dom.ts

@@ -0,0 +1,9 @@
+export function findFirstElement(selector: string): HTMLElement | null {
+	const elements = document.querySelectorAll(selector);
+	return elements.length > 0 ? elements[0] as HTMLElement : null;
+}
+
+export function findFirstChildElement(selector: string, root: Element): HTMLElement | null {
+	const elements = root.querySelectorAll(selector);
+	return elements.length > 0 ? elements[0] as HTMLElement : null;
+}