feat(map): add edge-center delta stats, thickness overlay, and layout fix

- Add edge-center sensor pair tables and delta calculations per wafer family.
- Parse and interpolate wafer thickness CSV data for offscreen visualization.
- Refactor ReadoutPanel layout using Item + anchors to fix right-margin clipping.
- Compact E-C Delta text format to fit standard sidebar width.
- Add pytest suite covering delta calculations, layout pairs, and thickness CSV.

src/pygui/backend/models/frame_stats.py

@@ -14,6 +14,44 @@ class Stats:
     sigma: float; three_sigma: float
 
 
+@dataclass(frozen=True)
+class EdgeCenterStats:
+    min_edge_index: int; min_center_index: int
+    min_edge: float; min_center: float; min_delta: float
+    max_edge_index: int; max_center_index: int
+    max_edge: float; max_center: float; max_delta: float
+
+
+def compute_edge_center(
+    values: list[float],
+    pairs: tuple[tuple[int, int], ...],
+    excluded: set[int],
+) -> EdgeCenterStats | None:
+    """Min/max |edge - center| over the family's pair table.
+
+    Pairs with an excluded (replaced) sensor, an index outside the frame, or a
+    NaN value are skipped. Returns None when no pair is computable.
+    """
+    n = len(values)
+    best: list[tuple[float, int, int]] = []
+    for e, c in pairs:
+        if e in excluded or c in excluded or e >= n or c >= n:
+            continue
+        if math.isnan(values[e]) or math.isnan(values[c]):
+            continue
+        best.append((abs(values[e] - values[c]), e, c))
+    if not best:
+        return None
+    min_d, min_e, min_c = min(best)
+    max_d, max_e, max_c = max(best)
+    return EdgeCenterStats(
+        min_edge_index=min_e, min_center_index=min_c,
+        min_edge=values[min_e], min_center=values[min_c], min_delta=min_d,
+        max_edge_index=max_e, max_center_index=max_c,
+        max_edge=values[max_e], max_center=values[max_c], max_delta=max_d,
+    )
+
+
 def compute_stats(values: list[float]) -> Stats:
     clean = [(i, v) for i, v in enumerate(values) if not math.isnan(v)]
     if not clean:

src/pygui/backend/models/sensor_editor.py

@@ -28,6 +28,11 @@ class SensorEditor:
     def has_overrides(self) -> bool:
         return bool(self._replacements or self._offsets)
 
+    def replaced_indices(self) -> set[int]:
+        """Sensors whose value is a replacement (offsets don't count — an
+        offset sensor still reads from its physical location)."""
+        return set(self._replacements)
+
     def active_indices(self) -> list[int]:
         """Return sorted sensor indices that have any override."""
         return sorted(set(self._replacements) | set(self._offsets))