feat: update settings management to use site_name and add batch update schema

backend/src/routes/setup.ts

@@ -14,7 +14,7 @@ const router = Router()
 const SALT_ROUNDS = 10
 
 function getSiteTitle(): string | null {
-  return settingsRepo.getSetting('site_title') ?? null
+  return settingsRepo.getSetting('site_name') ?? null
 }
 
 // GET /api/setup/status
@@ -38,7 +38,7 @@ router.post(
 
     // Atomic transaction prevents race conditions between concurrent setup requests
     const tx = db.transaction(() => {
-      const title = settingsRepo.getSetting('site_title')
+      const title = settingsRepo.getSetting('site_name')
       if (title) {
         throw new AppError(400, 'Setup already completed')
       }
@@ -74,7 +74,7 @@ router.post(
       })
 
       const settings: Array<[string, string]> = [
-        ['site_title', siteTitle?.trim() || 'BrainWave'],
+        ['site_name', siteTitle?.trim() || 'BrainWave'],
         ['site_language', language || 'en'],
         ['maintenance_mode', 'false'],
       ]