fix: remove updated_at from app_settings inserts in multiple migrations

The app_settings table in production doesn't have created_at/updated_at columns.
Fixed inconsistent usage across migrations:
- Migration 014: removed updated_at: new Date()
- Migration 027: removed updated_at: knex.fn.now()
- Migration 033: removed updated_at: new Date()

This ensures all migrations are consistent and won't fail in production.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/migrations/014_add_default_welcome_message.js

@@ -8,8 +8,7 @@ exports.up = async function(knex) {
     await knex('app_settings').insert({
       setting_key: 'general_default_welcome_message',
       setting_value: JSON.stringify('Thank you for using our photo sharing service! We hope you enjoy your photos.'),
-      setting_type: 'general',
-      updated_at: new Date()
+      setting_type: 'general'
     });
   }