Add vmamba_tiny.pth (VMamba-T `model` entry of U-Stone vmamba_tiny_e292.pth as a plain state_dict, 212 tensors) and merge it into manifest.json (tools/convert_backbone_weights.py)

backbones: plain state_dict re-hosts of torchvision resnet34 and U-Stone vmamba_small (weights_only-loadable), with manifest

initial commit