feat(invite-system): implement user invite functionality with registration mode control

server/routes/branding.js

@@ -82,11 +82,14 @@ router.get('/', async (req, res) => {
     const defaultTheme = await getSetting('default_theme');
     const logoFile = findLogoFile();
 
+    const registrationMode = await getSetting('registration_mode');
+
     res.json({
       appName: appName || 'Redlight',
       hasLogo: !!logoFile,
       logoUrl: logoFile ? '/api/branding/logo' : null,
       defaultTheme: defaultTheme || null,
+      registrationMode: registrationMode || 'open',
     });
   } catch (err) {
     log.branding.error('Get branding error:', err);
@@ -192,4 +195,19 @@ router.put('/default-theme', authenticateToken, requireAdmin, async (req, res) =
   }
 });
 
+// PUT /api/branding/registration-mode - Set registration mode (admin only)
+router.put('/registration-mode', authenticateToken, requireAdmin, async (req, res) => {
+  try {
+    const { registrationMode } = req.body;
+    if (!registrationMode || !['open', 'invite'].includes(registrationMode)) {
+      return res.status(400).json({ error: 'registrationMode must be "open" or "invite"' });
+    }
+    await setSetting('registration_mode', registrationMode);
+    res.json({ registrationMode });
+  } catch (err) {
+    log.branding.error('Update registration mode error:', err);
+    res.status(500).json({ error: 'Could not update registration mode' });
+  }
+});
+
 export default router;