Fix file copy location to respect configured media directory

Previously, files were always being copied to /media/audiobooks regardless
of the configured media directory in settings. This was caused by:

1. FileOrganizer singleton reading from MEDIA_DIR env var (never set)
   instead of database config 'media_dir'
2. Hardcoded /media/audiobooks fallback being used when env var not found
3. Three locations passing hardcoded paths to addOrganizeJob (unused)

Changes:
- Modified getFileOrganizer() to read media_dir from database config
- Made targetPath parameter optional in addOrganizeJob (not used by processor)
- Removed hardcoded /media/audiobooks paths from all addOrganizeJob calls
- Updated organize-files processor to await getFileOrganizer()
- Updated documentation to reflect configuration behavior

Files now correctly copy to the directory configured in setup wizard or
settings page, with /media/audiobooks only as fallback if not configured.

Fixes: User-reported issue where configured media directory was ignored

src/lib/processors/retry-failed-imports.processor.ts

@@ -72,8 +72,7 @@ export async function processRetryFailedImports(payload: RetryFailedImportsPaylo
         await jobQueue.addOrganizeJob(
           request.id,
           request.audiobook.id,
-          downloadPath,
-          `/media/audiobooks/${request.audiobook.author}/${request.audiobook.title}`
+          downloadPath
         );
         triggered++;
         await logger?.info(`Triggered organize job for request ${request.id}: ${request.audiobook.title}`);