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/utils/file-organizer.ts

@@ -464,16 +464,18 @@ export class FileOrganizer {
   }
 }
 
-// Singleton instance
-let fileOrganizer: FileOrganizer | null = null;
+/**
+ * Get FileOrganizer instance configured from database settings
+ * Reads media_dir from database configuration, falls back to /media/audiobooks if not configured
+ */
+export async function getFileOrganizer(): Promise<FileOrganizer> {
+  // Read media_dir from database config
+  const config = await prisma.configuration.findUnique({
+    where: { key: 'media_dir' },
+  });
 
-export function getFileOrganizer(): FileOrganizer {
-  if (!fileOrganizer) {
-    const mediaDir = process.env.MEDIA_DIR || '/media/audiobooks';
-    const tempDir = process.env.TEMP_DIR || '/tmp/readmeabook';
+  const mediaDir = config?.value || process.env.MEDIA_DIR || '/media/audiobooks';
+  const tempDir = process.env.TEMP_DIR || '/tmp/readmeabook';
 
-    fileOrganizer = new FileOrganizer(mediaDir, tempDir);
-  }
-
-  return fileOrganizer;
+  return new FileOrganizer(mediaDir, tempDir);
 }