fix: resolve old checkpoint path relative to repo root

Previously used a relative path that would fail depending on CWD.
Now resolved via __file__ to always point to the correct pretrained_weights/ directory.

test_app/app.py

@@ -57,8 +57,13 @@ def _load_old_model():
     device = old_cfg["device"]
     if not torch.cuda.is_available():
         device = "cpu"
+    # Resolve checkpoint path relative to repo root (one level up from test_app/)
+    ckpt_rel = old_cfg["checkpoint_path"]
+    ckpt_path = os.path.join(os.path.dirname(os.path.dirname(__file__)), ckpt_rel)
+    if not os.path.exists(ckpt_path):
+        raise FileNotFoundError(f"Checkpoint not found: {ckpt_path}")
     model = OldViTClassifier(old_cfg, device=device)
-    ckpt = torch.load(old_cfg["checkpoint_path"], map_location=device, weights_only=False)
+    ckpt = torch.load(ckpt_path, map_location=device, weights_only=False)
     model.load_state_dict(ckpt["model"])
     return model.to(device).eval()