Refactor username handling in API and v2 routes for improved normalization

v2Routes.js

@@ -149,6 +149,18 @@ function fixDataUri(dataUri) {
     }
 }
 
+function normalizeUsername(username) {
+    if (!username) return undefined;
+
+    const trimmed = username.trim();
+
+    // If empty or just "@", return undefined
+    if (!trimmed || trimmed === '@') return undefined;
+
+    // Add @ if it doesn't start with it
+    return trimmed.startsWith('@') ? trimmed : `@${trimmed}`;
+}
+
 
 const TEMPLATE_PATH = path.join(__dirname, 'template.html');
 const templateHtml = fs.readFileSync(TEMPLATE_PATH, 'utf8');
@@ -207,11 +219,9 @@ async function generateQuoteBuffer(config) {
 // POST /v2/quote - create new session
 router.post('/quote', (req, res) => {
     try {
-        const username = req.body.username?.trim();
-
         const data = {
             displayName: req.body.displayName?.trim(),
-            username: (username && username !== "@") ? username : undefined,
+            username: normalizeUsername(req.body.username),
             text: req.body.text,
             avatarUrl: fixDataUri(req.body.avatarUrl),
             imageUrl: fixDataUri(req.body.imageUrl),
@@ -254,8 +264,7 @@ router.patch('/quote/:id', (req, res) => {
 
         if (req.body.displayName !== undefined) data.displayName = req.body.displayName?.trim();
         if (req.body.username !== undefined) {
-            const username = req.body.username?.trim();
-            data.username = (username && username !== "@") ? username : undefined;
+            data.username = normalizeUsername(req.body.username);
         }
         if (req.body.text !== undefined) data.text = req.body.text;
         if (req.body.avatarUrl !== undefined) data.avatarUrl = fixDataUri(req.body.avatarUrl);