Align code with polygon-only training

configs/sampoly_polygon_head.json

@@ -0,0 +1,45 @@
+{
+  "model_name": "marine_sampoly_polygon",
+  "purpose": "Typical marine ecological feature polygon extraction",
+  "encoder": {
+    "type": "DINOv3 ViT + DINOv3 ConvNeXt dual branch",
+    "fusion": "Coast-style cross-scale semantic/detail fusion",
+    "fine_tuning": {
+      "vit_unfrozen_blocks": 2,
+      "convnext_unfrozen_stages": 2,
+      "unfreeze_all_norm_layers": true
+    }
+  },
+  "head": {
+    "style": "SAMPolyBuild-like polygon mapping",
+    "not_a_box_detector": true,
+    "outputs": [
+      "foreground_mask_logits",
+      "boundary_logits",
+      "vertex_logits",
+      "polygon_objectness",
+      "fixed_vertex_polygons"
+    ],
+    "default_num_queries": 100,
+    "default_vertices_per_polygon": 32,
+    "supervision": [
+      "mask",
+      "boundary",
+      "vertex_heatmap",
+      "polygon_sequence"
+    ]
+  },
+  "data": {
+    "preferred_formats": [
+      "images/{split} + masks/{split}",
+      "images/{split} + annotations/{split}.json",
+      "images/{split} + annotations/ann.json"
+    ],
+    "polygon_annotation_format": "COCO segmentation polygons",
+    "bbox_only_data": "not sufficient for true polygon training; reject from the main dataset"
+  },
+  "notes": [
+    "Training this head requires masks or polygon annotations; rectangle boxes cannot teach true boundaries.",
+    "Do not assume external coastline, land mask, or GIS vector layers are available."
+  ]
+}