fix: improve admin credentials display and configuration

- Display email address instead of username in migration output
- Use environment variables for admin email configuration
- Update deployment guide with clear admin setup instructions
- Add note that login requires email address, not username
- Fix GitHub URL to correct repository
- Remove obsolete version field from docker-compose.yml

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

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

backend/migrations/core/001_init.js

@@ -18,9 +18,13 @@ exports.up = async function(knex) {
       const generatedPassword = generateReadablePassword();
       const passwordHash = await bcrypt.hash(generatedPassword, 12); // Increased rounds for better security
       
+      // Get admin credentials from environment or use defaults
+      const adminUsername = process.env.ADMIN_USERNAME || 'admin';
+      const adminEmail = process.env.ADMIN_EMAIL || 'admin@example.com';
+      
       await knex('admin_users').insert({
-        username: 'admin',
-        email: 'admin@example.com',
+        username: adminUsername,
+        email: adminEmail,
         password_hash: passwordHash,
         created_at: new Date()
       });
@@ -36,7 +40,7 @@ PicPeak Admin Credentials
 
 Your admin account has been created with these credentials:
 
-Username: admin
+Email: ${adminEmail}
 Password: ${generatedPassword}
 
 IMPORTANT SECURITY NOTES:
@@ -47,6 +51,8 @@ IMPORTANT SECURITY NOTES:
 
 Login URL: ${process.env.ADMIN_URL || 'http://localhost:3001'}/admin
 
+Login with the email address shown above
+
 Generated on: ${new Date().toISOString()}
 ========================================
 `;
@@ -65,7 +71,7 @@ Generated on: ${new Date().toISOString()}
       console.log('\n========================================');
       console.log('✅ Admin user created successfully!');
       console.log('========================================');
-      console.log('Username: admin');
+      console.log(`Email: ${adminEmail}`);
       console.log(`Password: ${generatedPassword}`);
       console.log('\n⚠️  IMPORTANT:');
       console.log('1. Save these credentials securely');