chore(components): add LoadingCycle, DiscordAvatar and User, improve Button (@fehmer) (monkeytypegame#7463)

- **add isActive and classList to Button, move H2 and H3 to Headers**
- **add aria-label and router-link to button**
- **move tests to correct folders**
- **add LoadingCircle**
- **add DiscordAvatar and User**

Author: fehmer

frontend/__tests__/components/Button.spec.tsx

@@ -1,7 +1,7 @@
 import { render } from "@solidjs/testing-library";
 import { describe, it, expect, vi, beforeEach } from "vitest";
 
-import { AnimatedModal } from "../../src/ts/components/common/AnimatedModal";
+import { AnimatedModal } from "../../../src/ts/components/common/AnimatedModal";
 
 describe("AnimatedModal", () => {
   beforeEach(() => {