Fix React error #130 by correcting Card component usage

- Fixed all Card components to use padding prop instead of className
- Updated padding values: p-4 -> sm, p-6 -> md, p-8 -> lg
- This resolves the React element type invalid error

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

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

backend/src/database/db.js

@@ -100,8 +100,10 @@ async function initializeDatabase() {
     const hasUpdatedAt = await db.schema.hasColumn('admin_users', 'updated_at');
     if (!hasUpdatedAt) {
       await db.schema.table('admin_users', (table) => {
-        table.datetime('updated_at').defaultTo(db.fn.now());
+        table.datetime('updated_at');
       });
+      // Set default value for existing rows
+      await db('admin_users').update({ updated_at: new Date() });
     }
   }