Function writeFile

writeFile(
    buffer: Buffer,
    originalFilename: string,
    config: FileServingConfig,
): Promise<FileReservation>
Write a complete file buffer to storage

Convenience wrapper around reserveFile() for non-streaming use cases. Generates ID, formats filename, creates directory, and writes file atomically.
Parameters
- buffer: Buffer
  File content as a Buffer
- originalFilename: string
  Original filename to preserve
- config: FileServingConfig
  File serving configuration
Returns Promise<FileReservation>
FileReservation with id, storedName, and fullPath
Example
```
const pdfBuffer = Buffer.from('...');
const result = await writeFile(pdfBuffer, 'report.pdf', {
  resourceStoreUri: 'file:///tmp/files'
});
// result.storedName => '{uuid}-report.pdf'
// result.fullPath => '/tmp/files/{uuid}-report.pdf'
```
- Defined in src/file-serving/utils.ts:170