Implement markdown page for themes documentation

Author: JackTench

src/app/themes.tsx

@@ -0,0 +1,9 @@
+import { AppGitHubThemes } from "@/components/libresplit/AppGitHubThemes";
+
+export function Themes() {
+  return (
+    <div>
+      <AppGitHubThemes />
+    </div>
+  );
+}

src/components/libresplit/AppGitHubThemes.tsx

@@ -0,0 +1,33 @@
+import { useEffect, useState } from "react";
+
+import { AppLoading } from "./AppLoading";
+import { Markdown } from "@/lib/markdown";
+
+export function AppGitHubThemes() {
+  const [themes, setThemes] = useState<string>("Loading...");
+  const [isLoading, setIsLoading] = useState(true);
+
+  const urlThemes =
+    "https://raw.githubusercontent.com/LibreSplit/LibreSplit/refs/heads/main/docs/themes.md";
+
+  useEffect(() => {
+    fetch(urlThemes)
+      .then((res) => {
+        if (!res.ok) throw new Error(`HTTP Error! Status: ${res.status}`);
+        return res.text();
+      })
+      .then((text) => setThemes(text))
+      .catch(() => setThemes("Failed to load README from GitHub."))
+      .finally(() => setIsLoading(false));
+  }, []);
+
+  if (isLoading) {
+    return <AppLoading />;
+  }
+
+  return (
+    <div>
+      <Markdown content={themes} />
+    </div>
+  );
+}

src/router.tsx

@@ -1,6 +1,7 @@
 import { Converter } from "./app/converter";
 import { Home } from "./app/home";
 import { NotFound } from "./app/not-found";
+import { Themes } from "./app/themes";
 import { Route, Routes } from "react-router";
 
 export default function AppRouter() {
@@ -9,6 +10,9 @@ export default function AppRouter() {
       <Route path="/" element={<Home />} />
       <Route path="/converter" element={<Converter />} />
 
+      {/* Documentation Pages */}
+      <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 />} />
     </Routes>