Fix permission error when writing admin credentials

- Changed credential file location from /app/ to /app/data/
- Added directory creation with recursive flag
- Updated console messages to show correct file location
- The data/ directory is already owned by nodejs user in Dockerfile

The error occurred because the nodejs user doesn't have write
permission to /app/ directory, but does have permission to /app/data/
which is explicitly created and chowned in the Dockerfile.

DEPLOYMENT_GUIDE.md

@@ -180,7 +180,7 @@ docker-compose up -d
 # Run database migrations
 docker-compose exec backend npm run migrate
 
-# Admin credentials will be displayed and saved to ADMIN_CREDENTIALS.txt
+# Admin credentials will be displayed and saved to /data/ADMIN_CREDENTIALS.txt
 ```
 
 #### Step 4: Configure Nginx

backend/migrations/core/001_init.js

@@ -26,7 +26,15 @@ exports.up = async function(knex) {
       });
       
       // Save the generated password to a file for the user to retrieve
-      const setupInfoPath = path.join(__dirname, '..', '..', 'ADMIN_CREDENTIALS.txt');
+      const dataDir = path.join(__dirname, '..', '..', 'data');
+      const setupInfoPath = path.join(dataDir, 'ADMIN_CREDENTIALS.txt');
+      
+      // Ensure data directory exists
+      try {
+        await fs.mkdir(dataDir, { recursive: true });
+      } catch (error) {
+        // Directory might already exist, that's okay
+      }
       const setupInfo = `
 ========================================
 PicPeak Admin Credentials
@@ -58,8 +66,8 @@ Generated on: ${new Date().toISOString()}
       console.log(`Password: ${generatedPassword}`);
       console.log('\n⚠️  IMPORTANT:');
       console.log('1. Save these credentials securely');
-      console.log('2. You will be required to change the password on first login');
-      console.log('3. Credentials are also saved in: ADMIN_CREDENTIALS.txt');
+      console.log('2. Please change the password after first login');
+      console.log('3. Credentials are also saved in: data/ADMIN_CREDENTIALS.txt');
       console.log('========================================\n');
     }