Use NAS as primary storage — direct upload when enabled

When NAS storage is enabled, uploaded files go directly to the NAS share
(users/{username}/videos/{title-slug}/) with no permanent local copy kept.
Thumbnails and video are fetched from NAS on demand for streaming/playback.
When NAS is disabled, files are organised into the same directory schema
in local storage.

- VideoController: branch upload flow on NAS enabled/disabled
- NasSyncService: add uploadDirectToNas() for direct NAS writes,
  organizeLocalFiles() for local NAS-schema, localVideoDir() resolver,
  deleteLocalAssets() for post-sync cleanup
- GenerateHlsJob: download from NAS via ensureLocalCopy() when local
  file is absent (NAS-primary mode); clean up temp after HLS generation
- CompressVideoJob: place compressed file alongside original (any dir)
- Video/VideoSlide models: localVideoPath(), localThumbnailPath(),
  thumbnailStorageKey(), localPath(), storageKey() helpers for
  format-agnostic path resolution (old flat paths + new NAS-schema paths)
- MediaController: serve thumbnails from NAS-mirrored paths with NAS fallback
- SuperAdminController: use model path helpers for file deletion
- NasFreeLocalStorage: scan new users/ tree in addition to legacy flat dirs
- Settings: rename "NAS Storage Sync" tab to "NAS Storage", update description

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

app/Models/VideoSlide.php

@@ -15,6 +15,28 @@ class VideoSlide extends Model
 
     public function getUrlAttribute(): string
     {
-        return asset('storage/thumbnails/' . $this->filename);
+        return route('media.thumbnail', $this->filename);
+    }
+
+    /**
+     * Absolute path to the slide image on local disk.
+     * Old format: storage/app/public/thumbnails/{filename}
+     * New format: storage/app/{relative-path}  (filename contains a slash)
+     */
+    public function localPath(): string
+    {
+        return str_contains($this->filename, '/')
+            ? storage_path('app/' . $this->filename)
+            : storage_path('app/public/thumbnails/' . $this->filename);
+    }
+
+    /**
+     * Storage::delete()-compatible key for this slide file.
+     */
+    public function storageKey(): string
+    {
+        return str_contains($this->filename, '/')
+            ? $this->filename
+            : 'public/thumbnails/' . $this->filename;
     }
 }