Add root config.json (architecture of every variant) for download counting

The Hub counts a model download for every request to a root `config.json`; the repo has only `.pth` files, so DeFM currently shows 0 downloads. This adds a `config.json` with the architecture config of all 12 variants (generated from `defm/configs/*.yaml` by `scripts/hf/build_model_config.py`). Nothing reads it yet; the defm package will fetch it before the weights from the next release. No existing file changes.

config.json

@@ -0,0 +1,90 @@
+{
+  "model_type": "defm",
+  "library_name": "defm",
+  "variants": {
+    "defm_efficientnet_b0": {
+      "arch": "efficientnet_b0",
+      "out_channels": 64
+    },
+    "defm_efficientnet_b2": {
+      "arch": "efficientnet_b2",
+      "out_channels": 128
+    },
+    "defm_efficientnet_b4": {
+      "arch": "efficientnet_b4",
+      "out_channels": 256
+    },
+    "defm_efficientnet_b6": {
+      "arch": "efficientnet_b6",
+      "out_channels": 256
+    },
+    "defm_regnet_y_1_6gf": {
+      "arch": "regnet_y_1_6gf",
+      "out_channels": 256
+    },
+    "defm_regnet_y_400mf": {
+      "arch": "regnet_y_400mf",
+      "out_channels": 64
+    },
+    "defm_regnet_y_800mf": {
+      "arch": "regnet_y_800mf",
+      "out_channels": 128
+    },
+    "defm_resnet18": {
+      "arch": "resnet18",
+      "out_channels": 128
+    },
+    "defm_resnet34": {
+      "arch": "resnet34",
+      "out_channels": 256
+    },
+    "defm_resnet50": {
+      "arch": "resnet50",
+      "out_channels": 256
+    },
+    "defm_vit_l14": {
+      "arch": "vit_large",
+      "patch_size": 14,
+      "in_chans": 3,
+      "layerscale": 1e-05,
+      "ffn_layer": "swiglufused",
+      "block_chunks": 4,
+      "qkv_bias": true,
+      "proj_bias": true,
+      "ffn_bias": true,
+      "num_register_tokens": 0,
+      "interpolate_antialias": false,
+      "interpolate_offset": 0.1,
+      "global_crops_size": 224
+    },
+    "defm_vit_s14": {
+      "arch": "vit_small",
+      "patch_size": 14,
+      "in_chans": 3,
+      "layerscale": 1e-05,
+      "ffn_layer": "swiglufused",
+      "block_chunks": 4,
+      "qkv_bias": true,
+      "proj_bias": true,
+      "ffn_bias": true,
+      "num_register_tokens": 0,
+      "interpolate_antialias": false,
+      "interpolate_offset": 0.1,
+      "global_crops_size": 224
+    }
+  },
+  "weights": {
+    "defm_efficientnet_b0": "defm_efficientnet_b0.pth",
+    "defm_efficientnet_b2": "defm_efficientnet_b2.pth",
+    "defm_efficientnet_b4": "defm_efficientnet_b4.pth",
+    "defm_efficientnet_b6": "defm_efficientnet_b6.pth",
+    "defm_regnet_y_1_6gf": "defm_regnet_y_1_6gf.pth",
+    "defm_regnet_y_400mf": "defm_regnet_y_400mf.pth",
+    "defm_regnet_y_800mf": "defm_regnet_y_800mf.pth",
+    "defm_resnet18": "defm_resnet18.pth",
+    "defm_resnet34": "defm_resnet34.pth",
+    "defm_resnet50": "defm_resnet50.pth",
+    "defm_vit_l14": "defm_vit_l14.pth",
+    "defm_vit_s14": "defm_vit_s14.pth"
+  }
+}