refactor: reorganize backend modules into sub-packages for models, data, visualization, wafer, and controllers

src/pygui/backend/models/frame.py

@@ -0,0 +1,11 @@
+from __future__ import annotations
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class Frame:
+    """One sample across all sensors ata a point in time"""
+
+    seq: int            # monotonically increasing
+    time: float             # seconds (relative or epoch)
+    values: list[float]  # one per sensor, in sensor-layout order