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/organize-files.processor.ts

@@ -43,8 +43,8 @@ export async function processOrganizeFiles(payload: OrganizeFilesPayload): Promi
 
     await logger?.info(`Organizing: ${audiobook.title} by ${audiobook.author}`);
 
-    // Get file organizer
-    const organizer = getFileOrganizer();
+    // Get file organizer (reads media_dir from database config)
+    const organizer = await getFileOrganizer();
 
     // Organize files (pass logger to file organizer)
     const result = await organizer.organize(