feat(backend): introduce session controller and status models

Implement DeviceController and SessionController to bridge QML requests with backend state, supporting playback replay tracking, cluster averaging, and slot error boundaries.

src/pygui/backend/comparison.py

@@ -17,8 +17,14 @@ Returns:
     x = np.array(series_a, dtype=float)
     y = np.array(series_b, dtype=float)
 
-    if x.size == 0 or y.size == 0:
-        return {"distance": float('inf'), "index_a": [],"index_b": [], "warping_path": []}
+    # Filter out NaN/Inf values so dtw doesn't choke on them.
+    mask_x = np.isfinite(x)
+    mask_y = np.isfinite(y)
+    if not mask_x.any() or not mask_y.any():
+        return {"distance": float('inf'), "index_a": [], "index_b": [], "warping_path": []}
+
+    x = x[mask_x]
+    y = y[mask_y]
 
     alignment = dtw(x, y, keep_internals=True)
     return {