- added iso sheet for tech draw

src/fluency/ui/technical_drawing_widget.py

@@ -54,8 +54,9 @@ from fluency.technical_drawing import (
 )
 
 # Sheet layout constants.
-_A3_MM_W = 420.0
-_A3_MM_H = 297.0
+# Sheet layout constants (A4 landscape, ISO 5457 template).
+_A4_MM_W = 297.0
+_A4_MM_H = 210.0
 
 
 # ── 2D geometry helpers (view-plane model coordinates) ────────────────────
@@ -202,7 +203,7 @@ class DrawingCanvas(QWidget):
 
     def _sheet_rect(self) -> QRectF:
         """Sheet rect in device coordinates (zoom/pan applied)."""
-        aspect = _A3_MM_W / _A3_MM_H
+        aspect = _A4_MM_W / _A4_MM_H
         w = self.width()
         h = self.height()
 
@@ -220,18 +221,18 @@ class DrawingCanvas(QWidget):
     def to_sheet(self, pos: QPointF) -> Tuple[float, float]:
         """Convert a device pixel position to sheet mm coordinates."""
         rect = self._sheet_rect()
-        scale = rect.width() / _A3_MM_W
+        scale = rect.width() / _A4_MM_W
         if scale <= 0:
             return (0.0, 0.0)
         return (
             (pos.x() - rect.x()) / scale,
-            _A3_MM_H - (pos.y() - rect.y()) / scale,
+            _A4_MM_H - (pos.y() - rect.y()) / scale,
         )
 
     def _pick_tolerance_mm(self) -> float:
         """Pick radius in sheet mm (about 6 device pixels)."""
         rect = self._sheet_rect()
-        scale = rect.width() / _A3_MM_W
+        scale = rect.width() / _A4_MM_W
         return 6.0 / scale if scale > 0 else 6.0
 
     def _sheet_to_model(