Restructure into src/ layout under pygui package

Move all application source under src/pygui/ and rewire imports,
build config, and QML module path to match.
- Relocate backend/, serialcomm/, and the ISC QML module into
  src/pygui/; convert main.py into pygui/__main__.py with a main()
  entry point (run via `python -m pygui` or the new `isc` script)
- Rewrite absolute imports: backend.* -> pygui.backend.*,
  serialcomm.* -> pygui.serialcomm.* (source + tests)
- Move app icons (isc.ico/icns) into packaging/
- Update README and ISC.qmlproject to the new paths

src/pygui/backend/zwafer_parser.py

@@ -0,0 +1,131 @@
+from pathlib import Path
+from typing import Tuple, Optional
+from datetime import datetime, timedelta
+
+from pygui.backend.zwafer_models import ZWaferData, Sensor
+
+
+# ===== Z-Wafer CSV Parser =====
+class ZWaferParser:
+    """Parses Z-wafer CSV files (header + sensor layout + data rows)."""
+
+    # ===== Public Parse API =====
+    def parse(self, file_path: str) -> Tuple[Optional[ZWaferData], Optional[Path]]:
+        """
+        Parse a Z-wafer file.
+
+        Returns:
+            (ZWaferData, Path) on success
+            (None, None) on error (e.g., file not found)
+        """
+        try:
+            path = Path(file_path)
+            if not path.exists():
+                raise FileNotFoundError(f"File not found: {file_path}")
+
+            with path.open("r", encoding="utf-8") as f:
+                return self._process_header(f), path
+        except (ValueError, KeyError):
+            raise
+        except Exception:
+            return None, None
+
+    # ===== Header Parsing =====
+    def _process_header(self, file_obj) -> ZWaferData:
+        """Parse header and sensor layout from open file object."""
+        wafer_data = ZWaferData()
+        labels: Optional[list] = None
+        x_coords: Optional[list] = None
+        y_coords: Optional[list] = None
+
+        for line in file_obj:
+            # Strip trailing comma + whitespace
+            line = line.rstrip().rstrip(",").strip()
+            if not line or line.replace(",", "").strip() == "":
+                continue
+
+            parts = [p.strip() for p in line.split(",")]
+            first_part = parts[0].lower()
+
+            # Detect end of header section
+            if first_part == "data":
+                wafer_data.csv_headers = labels or []
+                self._build_sensor_layout(wafer_data, labels, x_coords, y_coords)
+                return wafer_data
+
+            # Detect switch from metadata to sensor layout
+            # Parse metadata (key=value pairs)
+            if not self._parse_header_line(wafer_data, parts):
+                # If not metadata, it's part of sensor layout
+                label = parts[0].lower()
+                values = parts[1:]
+
+                if label == "label":
+                    labels = values
+                elif label == "x (mm)":
+                    x_coords = values
+                elif label == "y (mm)":
+                    y_coords = values
+
+        return wafer_data  # Incomplete file — return partial data
+
+    # ===== Metadata Parsing =====
+    def _parse_header_line(self, wafer_data: ZWaferData, parts: list) -> bool:
+        """Parse key=value pairs from header line. Returns True if handled."""
+        non_empty_parts = [p for p in parts if p]
+        if not non_empty_parts:
+            return False
+
+        found_kv = False
+        for part in non_empty_parts:
+            eq_idx = part.find("=")
+            if eq_idx < 0:
+                continue
+
+            key = part[:eq_idx].strip()
+            value = part[eq_idx + 1 :].strip('=" ')
+            found_kv = True
+
+            wafer_data.header[key] = value
+
+            # Extract special fields
+            if key.lower() == "acquisition date":
+                try:
+                    from datetime import datetime as dt
+
+                    wafer_data.date = dt.strptime(value, "%m/%d/%Y")
+                except ValueError:
+                    wafer_data.date = datetime.min  # Fallback on parse error
+            elif key.lower() == "wafer id":
+                wafer_data.serial = value
+
+        if found_kv and wafer_data.date == datetime.min:
+            wafer_data.date = datetime.min
+
+        return found_kv
+
+    # ===== Sensor Layout Parsing =====
+    def _build_sensor_layout(
+        self,
+        wafer_data: ZWaferData,
+        labels: Optional[list],
+        x_coords: Optional[list],
+        y_coords: Optional[list],
+    ) -> None:
+        """Build sensor list from layout arrays."""
+        if not all([labels, x_coords, y_coords]):
+            raise ValueError("Sensor layout section is incomplete or missing.")
+
+        if len(labels) != len(x_coords) or len(labels) != len(y_coords):
+            raise ValueError(
+                f"Mismatched sensor columns: labels={len(labels)}, "
+                f"x={len(x_coords)}, y={len(y_coords)}"
+            )
+
+        for i in range(len(labels)):
+            try:
+                wafer_data.sensors.append(
+                    Sensor(label=labels[i], x=float(x_coords[i]), y=float(y_coords[i]))
+                )
+            except ValueError as e:
+                raise ValueError(f"Invalid coordinate at index {i}: {e}")