feat(stability): Módulo 3 — Curva GZ + criterios IMO IS Code 2008

- gz_integrator.py: GZCurve, GZPoint, compute_gz_wall_sided (fórmula
  pared lateral), compute_gz_direct (integración Sutherland-Hodgman)
- imo_is2008.py: IMOCriterion, IMOResult, check_imo_is2008 —
  6 criterios A.2.1.1–A.2.1.6 del IS Code 2008 Cap.2
- gz_curve_widget.py: GZCurveWidget QPainter — curva cian, áreas
  sombreadas, líneas IMO, marcador AVS, tabla PASS/FAIL integrada
- main_window.py: GZCurveWidget en MOD_STABILITY, _compute_and_show_gz,
  _on_show_stability conectado al ribbon
- dark.qss: estilos GZCurveWidget
- test_module3_stability.py: 33 tests S-01..S-28 (315 total, todos pasan)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

arshipdesign/ui/main_window.py

@@ -47,6 +47,8 @@ from PySide6.QtWidgets import (
 from arshipdesign import __version__
 from arshipdesign.core.project import Project
 from arshipdesign.utils.logger import get_logger
+from arshipdesign.stability import compute_gz_wall_sided, GZCurve, check_imo_is2008
+from arshipdesign.ui.widgets.gz_curve_widget import GZCurveWidget
 from arshipdesign.utils.settings import (
     add_recent_file,
     get_language,
@@ -813,6 +815,7 @@ class MainWindow(QMainWindow):
         super().__init__()
         self._project: Optional[Project] = None
         self._current_hull = None   # Hull activo en todos los visores
+        self._gz_widget: Optional[GZCurveWidget] = None
         self._lang = get_language()
         self._strings = _load_i18n(self._lang)
         self._setup_ui()
@@ -878,6 +881,10 @@ class MainWindow(QMainWindow):
         self._hydro_chart = HydrostaticsChartWidget()
         self._module_area.set_module_widget(ModuleArea.MOD_CURVES, self._hydro_chart)
 
+        # Módulo de estabilidad GZ (sustituye el placeholder MOD_STABILITY)
+        self._gz_widget = GZCurveWidget()
+        self._module_area.set_module_widget(ModuleArea.MOD_STABILITY, self._gz_widget)
+
         # Dock izquierdo — capas
         self._layers_panel = LayersPanel(self._strings)
         self._dock_layers = QDockWidget("Capas", self)
@@ -981,7 +988,7 @@ class MainWindow(QMainWindow):
 
         g = self._ribbon.new_group(RibbonBar.TAB_ANALYSIS, "Estabilidad")
         g.add_button(_spi(sp.SP_FileDialogDetailedView), "Curva GZ",   "Curva GZ estática",
-                     lambda: self._module_area.activate(M.MOD_STABILITY), False)
+                     self._on_show_stability)
         g.add_button(_spi(sp.SP_FileDialogDetailedView), "IMO IS2008", "Criterios IMO IS Code 2008", enabled=False)
         g.add_button(_spi(sp.SP_FileDialogDetailedView), "Avería",     "Estabilidad en avería",      enabled=False)
 
@@ -1114,7 +1121,7 @@ class MainWindow(QMainWindow):
                          slot=self._on_export_hydrostatics_csv)
 
         sm = m.addMenu("Estabilidad")
-        self._add_action(sm, "Curva GZ — Estabilidad estática", slot=lambda: self._module_area.activate(M.MOD_STABILITY),  enabled=False)
+        self._add_action(sm, "Curva GZ — Estabilidad estática", slot=self._on_show_stability)
         self._add_action(sm, "Criterios IMO IS Code 2008",                                                                    enabled=False)
         self._add_action(sm, "Criterio de viento A.749(18)",                                                                  enabled=False)
         self._add_action(sm, "Estabilidad en avería (SOLAS 2009)",                                                             enabled=False)
@@ -1330,6 +1337,8 @@ class MainWindow(QMainWindow):
                 logger.warning("No se pudo cargar hull en visor 3D: %s", exc)
         # ── Panel hidrostáticos ───────────────────────────────────
         self._update_hydrostatics(hull)
+        # ── Curva GZ (si el módulo está activo o precalcular) ─────
+        self._compute_and_show_gz()
 
     def _on_offsets_dragging(self, offsets_table) -> None:
         """Slot ligero — actualiza vistas 2D durante drag sin resetear zoom ni actualizar 3D."""
@@ -1474,6 +1483,44 @@ class MainWindow(QMainWindow):
             from PySide6.QtWidgets import QMessageBox
             QMessageBox.critical(self, "Error al exportar", str(exc))
 
+    # ─────────────────────────────────────────────────────────
+    # CURVA GZ — ESTABILIDAD
+    # ─────────────────────────────────────────────────────────
+
+    def _compute_and_show_gz(self) -> None:
+        """Calcula la curva GZ wall-sided y actualiza el widget de estabilidad."""
+        if self._current_hull is None:
+            return
+        if self._gz_widget is None:
+            return
+        try:
+            hull = self._current_hull
+            kg = hull.depth * 0.55
+            self.statusBar().showMessage("Calculando curva GZ…")
+            QApplication.processEvents()
+            gz_curve = compute_gz_wall_sided(hull, hull.draft, kg=kg)
+            imo_result = check_imo_is2008(gz_curve)
+            self._gz_widget.set_curve(gz_curve, imo_result)
+            # Actualizar indicador IMO en la barra de hidrostáticos
+            self._hydro.set_imo_status(
+                imo_result.overall_passed,
+                "" if imo_result.overall_passed else "GZ",
+            )
+            self.statusBar().showMessage(
+                f"Curva GZ calculada — {hull.name}  "
+                f"GM={gz_curve.gm:.3f}m  GZmax={gz_curve.gz_max:.3f}m  "
+                f"AVS={gz_curve.avs:.0f}°  "
+                f"IMO={'CUMPLE' if imo_result.overall_passed else 'FALLA'}"
+            )
+        except Exception as exc:
+            logger.warning("Error al calcular curva GZ: %s", exc)
+
+    def _on_show_stability(self) -> None:
+        """Muestra el módulo de estabilidad GZ (calcula si hay casco disponible)."""
+        if self._current_hull is not None:
+            self._compute_and_show_gz()
+        self._module_area.activate(ModuleArea.MOD_STABILITY)
+
     def _ask_save(self) -> bool:
         reply = QMessageBox.question(
             self, "Cambios sin guardar",