Fix right-click map menu opening at (0,0) instead of the cursor position

Gdk.Rectangle(x=..., y=..., width=..., height=...) silently ignores
every constructor keyword argument in this PyGObject version (verified
directly: it always built a zeroed rect regardless of what was passed
in), so popover.set_pointing_to() was always pointing at the canvas's
top-left corner. Fixed by constructing the rect and assigning its
fields afterward, which does work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/fenigma/app.py

@@ -1044,7 +1044,15 @@ class MainWindow(Adw.ApplicationWindow):
         you're pointing and don't need to type coordinates."""
         popover = Gtk.Popover()
         popover.set_parent(self.canvas)
-        popover.set_pointing_to(Gdk.Rectangle(x=int(x), y=int(y), width=1, height=1))
+        # NOT Gdk.Rectangle(x=..., y=..., ...): verified directly that this
+        # PyGObject version silently ignores every constructor keyword arg on
+        # boxed types like GdkRectangle (a real bug, not a style preference,
+        # it built a zeroed rect every time), which is exactly why this popover
+        # always opened pinned to the canvas's top-left corner instead of the
+        # actual click position. Assigning the fields after construction works.
+        rect = Gdk.Rectangle()
+        rect.x, rect.y, rect.width, rect.height = int(x), int(y), 1, 1
+        popover.set_pointing_to(rect)
         popover.connect("closed", lambda _p: popover.unparent())
 
         box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL, spacing=2,