fix: remap bare Sequential keys to net.* when loading ddg_da.pt

Checkpoint was saved when DriftPredictorMLP used a bare nn.Sequential,
producing keys like '0.weight'. Current class wraps it as self.net,
expecting 'net.0.weight'. Remap on load so old .pt files load correctly.

app/models/ddg_da.py

@@ -96,6 +96,10 @@ class DDGDAPredictor:
         if os.path.exists(model_path):
             try:
                 state = torch.load(model_path, map_location="cpu", weights_only=True)
+                # Remap bare Sequential keys ("0.weight") → nested ("net.0.weight")
+                # to handle checkpoints saved before the self.net wrapper was added.
+                if any(k.startswith("0.") or k.startswith("3.") for k in state):
+                    state = {f"net.{k}": v for k, v in state.items()}
                 self.mlp.load_state_dict(state)
                 self.mlp.eval()
             except Exception as e: