Introduce e2e test

src/client/instance.ts

@@ -25,6 +25,7 @@ export async function fetchInstance() {
 }
 
 export const emojiCategories = computed(() => {
+	if (instance.emojis == null) return [];
 	const categories = new Set();
 	for (const emoji of instance.emojis) {
 		categories.add(emoji.category);
@@ -33,6 +34,7 @@ export const emojiCategories = computed(() => {
 });
 
 export const emojiTags = computed(() => {
+	if (instance.emojis == null) return [];
 	const tags = new Set();
 	for (const emoji of instance.emojis) {
 		for (const tag of emoji.aliases) {