Implement themes docs page

Author: JackTench

src/app/themes.tsx

@@ -0,0 +1,9 @@
+import { AppGitHubGenericMarkdown } from "@/components/libresplit/AppGitHubGenericMarkdown";
+
+export function Themes() {
+  return (
+    <div>
+      <AppGitHubGenericMarkdown url="https://raw.githubusercontent.com/LibreSplit/LibreSplit/refs/heads/main/docs/themes.md" />
+    </div>
+  );
+}

src/router.tsx

@@ -4,6 +4,7 @@ import { Home } from "./app/home";
 import { NotFound } from "./app/not-found";
 import { SettingsKeybinds } from "./app/settings-keybinds";
 import { SplitFiles } from "./app/split-files";
+import { Themes } from "./app/themes";
 import { Route, Routes } from "react-router";
 
 export default function AppRouter() {
@@ -16,6 +17,7 @@ export default function AppRouter() {
       <Route path="/docs/auto-splitters.md" element={<AutoSplitters />} />
       <Route path="/docs/settings-keybinds.md" element={<SettingsKeybinds />} />
       <Route path="/docs/split-files.md" element={<SplitFiles />} />
+      <Route path="/docs/themes.md" element={<Themes />} />
 
       {/* Fall back on app's 404 page. This is because of the SPA routing trick with 404.html used in GitHub Pages. */}
       <Route path="*" element={<NotFound />} />