fix: file upload defaults private, internal network access, video inline

- _save_uploaded_file: keep is_public=False by default (no auto-public)
- PublicFileView: internal network (192.168/10/172.16-31) serves any file;
  external only serves is_public=True files
- Video files: Content-Disposition inline for browser playback
- DRF API: fix misleading error message (files not files[])

links/file_views.py

@@ -78,7 +78,7 @@ class FileDownloadView(View):
         if not os.path.exists(record.file_path):
             raise Http404("File not found on disk")
         FileUpload.objects.filter(pk=pk).update(download_count=F('download_count') + 1)
-        disposition = 'inline' if record.is_image else f'attachment; filename="{record.name}"'
+        disposition = 'inline' if (record.is_image or record.mime_type.startswith('video/')) else f'attachment; filename="{record.name}"'
         response = FileResponse(open(record.file_path, 'rb'), content_type=record.mime_type)
         response['Content-Disposition'] = disposition
         return response
@@ -131,14 +131,44 @@ class FileSetExpiryView(View):
 
 
 class PublicFileView(View):
+    """Serve uploaded files via /public/files/{uuid}-{name}.
+
+    Access rules:
+    - Internal network (192.168.x.x, 10.x.x.x, 172.16-31.x.x): serve any file
+    - External (go.junv.cc, xgo.junv.cc): only serve is_public=True files
+    - Videos and images stream inline; other files force download.
+    """
+
+    INTERNAL_NETS = ('192.168.', '10.', '172.16.', '172.17.', '172.18.',
+                     '172.19.', '172.20.', '172.21.', '172.22.', '172.23.',
+                     '172.24.', '172.25.', '172.26.', '172.27.', '172.28.',
+                     '172.29.', '172.30.', '172.31.')
+
+    def _is_internal(self, request):
+        xff = request.META.get('HTTP_X_FORWARDED_FOR', '')
+        client_ip = xff.split(',')[0].strip() if xff else request.META.get('REMOTE_ADDR', '')
+        return any(client_ip.startswith(net) for net in self.INTERNAL_NETS)
+
     def get(self, request, pk, filename=''):
-        record = get_object_or_404(FileUpload, pk=pk, is_public=True)
+        record = get_object_or_404(FileUpload, pk=pk)
+
+        # External access: only public files
+        if not self._is_internal(request) and not record.is_public:
+            raise Http404("This file is private")
+
         if record.is_expired:
-            raise Http404("This public link has expired")
+            raise Http404("This link has expired")
         if not os.path.exists(record.file_path):
             raise Http404("File not found")
+
         FileUpload.objects.filter(pk=record.pk).update(download_count=F('download_count') + 1)
-        disposition = 'inline' if record.is_image else f'attachment; filename="{record.name}"'
+
+        # Inline for media, attachment for everything else
+        if record.is_image or record.mime_type.startswith('video/'):
+            disposition = 'inline'
+        else:
+            disposition = f'attachment; filename="{record.name}"'
+
         response = FileResponse(open(record.file_path, 'rb'), content_type=record.mime_type)
         response['Content-Disposition'] = disposition
         return response
@@ -155,7 +185,7 @@ class FileUploadViewSet(viewsets.ModelViewSet):
     def create(self, request, *args, **kwargs):
         uploaded = request.FILES.getlist('files')
         if not uploaded:
-            return Response({'error': 'No files provided. Use files[] field.'}, status=status.HTTP_400_BAD_REQUEST)
+            return Response({'error': 'No files provided. Use "files" field.'}, status=status.HTTP_400_BAD_REQUEST)
         created = [_save_uploaded_file(f) for f in uploaded]
         serializer = self.get_serializer(created, many=True)
         return Response(serializer.data, status=status.HTTP_201_CREATED)
@@ -201,7 +231,7 @@ class FileUploadViewSet(viewsets.ModelViewSet):
         if not os.path.exists(record.file_path):
             raise Http404("File not found")
         FileUpload.objects.filter(pk=pk).update(download_count=F('download_count') + 1)
-        disposition = 'inline' if record.is_image else f'attachment; filename="{record.name}"'
+        disposition = 'inline' if (record.is_image or record.mime_type.startswith('video/')) else f'attachment; filename="{record.name}"'
         response = FileResponse(open(record.file_path, 'rb'), content_type=record.mime_type)
         response['Content-Disposition'] = disposition
         return response