refactor: remove dead files, dedupe formatBytes and document numbering helpers

- Delete unused adminEvents-enhanced.js, backupService.original.js,
  databaseBackup.example.js, s3Storage.example.js, ThemeCustomizer.tsx
- Extract shared formatBytes to utils/formatBytes.js (was copied 4x)
- Centralize formatNumberInTemplate + next-document-number logic in
  utils/documentSequences.js (was copied in invoice/quote/contract services)

backend/src/services/restoreService.js

@@ -12,6 +12,7 @@ const backupManifest = require('./backupManifest');
 const S3StorageAdapter = require('./storage/s3Storage');
 const { queueEmail } = require('./emailProcessor');
 const { formatBoolean } = require('../utils/dbCompat');
+const { formatBytes } = require('../utils/formatBytes');
 const os = require('os');
 
 /**
@@ -1528,15 +1529,7 @@ END $$;`
    * Format bytes to human readable
    */
   formatBytes(bytes, decimals = 2) {
-    if (bytes === 0) return '0 Bytes';
-    
-    const k = 1024;
-    const dm = decimals < 0 ? 0 : decimals;
-    const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
-    
-    const i = Math.floor(Math.log(bytes) / Math.log(k));
-    
-    return parseFloat((bytes / Math.pow(k, i)).toFixed(dm)) + ' ' + sizes[i];
+    return formatBytes(bytes, decimals);
   }
 
   /**