Add last_login column to users table migration

Changes:
- Add last_login TIMESTAMP column to existing users table
- Complete the users table migration with all required columns
- Fixes 500 error: Unknown column 'last_login' in 'INSERT INTO'

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server.js

@@ -47,16 +47,6 @@ async function initDatabase() {
     `);
 
     // Migrate existing users table to add missing columns
-    try {
-      await connection.query(`
-        ALTER TABLE users
-        ADD COLUMN IF NOT EXISTS display_name VARCHAR(255) AFTER username,
-        ADD COLUMN IF NOT EXISTS email VARCHAR(255) AFTER display_name,
-        ADD COLUMN IF NOT EXISTS groups TEXT AFTER email
-      `);
-      console.log('Users table migrated successfully');
-    } catch (error) {
-      // MariaDB doesn't support IF NOT EXISTS in ALTER TABLE, try individual columns
     try {
       await connection.query(`ALTER TABLE users ADD COLUMN display_name VARCHAR(255) AFTER username`);
     } catch (e) { /* Column exists */ }
@@ -66,8 +56,10 @@ async function initDatabase() {
     try {
       await connection.query(`ALTER TABLE users ADD COLUMN groups TEXT AFTER email`);
     } catch (e) { /* Column exists */ }
+    try {
+      await connection.query(`ALTER TABLE users ADD COLUMN last_login TIMESTAMP NULL AFTER groups`);
+    } catch (e) { /* Column exists */ }
     console.log('Users table migration completed');
-    }
 
     await connection.query(`
       CREATE TABLE IF NOT EXISTS workers (