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/Jobs/NasSyncVideoJob.php

@@ -30,6 +30,7 @@ class NasSyncVideoJob implements ShouldQueue
             // Video uploads must keep the local file until GenerateHlsJob finishes.
             if ($this->video->type === 'music') {
                 $nas->deleteLocalVideo($this->video);
+                $nas->deleteLocalAssets($this->video);
             }
         } catch (\Throwable $e) {
             \Illuminate\Support\Facades\Log::warning('NAS syncVideo failed for video ' . $this->video->id . ': ' . $e->getMessage());