Fallback to classic ttk when ttkbootstrap fails

app/gui/theme.py

@@ -31,12 +31,16 @@ class ThemeMixin:
         """Initialise ttk style handling and apply the detected theme."""
         if HAS_TTKBOOTSTRAP:
             try:
-                # Ensure msgcat package is available before ttkbootstrap initialises translations
+                try:
                     self.root.tk.call("package", "require", "msgcat")  # type: ignore[attr-defined]
                 except Exception:
                     pass
                 self.style = tb.Style()
                 self.using_tb = True
+            except Exception:
+                self.style = ttk.Style()
+                self.style.theme_use("clam")
+                self.using_tb = False
         else:
             self.style = ttk.Style()
             self.style.theme_use("clam")