Add missing markDirty()/markCompositeDirty() to all Python property setters

Fixes a systemic bug where Python tp_getset property setters bypassed the
render cache dirty flag system (#144). The animation/C++ setProperty() path
had correct dirty propagation, but direct Python property assignments
(e.g. frame.x = 50, caption.text = "Hello") did not invalidate the parent
Frame's render cache when clip_children or cache_subtree was enabled.

Changes by file:
- UIDrawable.cpp: Add markCompositeDirty() to set_float_member (x/y),
  set_pos, set_grid_pos; add markDirty() for w/h resize
- UICaption.cpp: Add markDirty() to set_text, set_color_member,
  set_float_member (outline/font_size); markCompositeDirty() for position
- UICollection.cpp: Add markContentDirty() on owner in append, remove,
  pop, insert, extend, setitem, and slice assignment/deletion
- UISprite.cpp: Add markDirty() to scale/sprite_index/texture setters;
  markCompositeDirty() to position setters
- UICircle.cpp: Add markDirty() to radius/fill_color/outline_color/outline;
  markCompositeDirty() to center setter
- UILine.cpp: Add markDirty() to start/end/color/thickness setters
- UIArc.cpp: Add markDirty() to radius/angles/color/thickness setters;
  markCompositeDirty() to center setter
- UIGrid.cpp: Add markDirty() to center/zoom/camera_rotation/fill_color/
  size/perspective/fov setters

Closes #288, closes #289, closes #290, closes #291

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

src/UIGrid.cpp

@@ -1074,7 +1074,8 @@ int UIGrid::set_size(PyUIGridObject* self, PyObject* value, void* closure) {
     tex_height = std::min(tex_height, 4096u);
     
     self->data->renderTexture.create(tex_width, tex_height);
-    
+    self->data->markDirty(); // #291: size change
+
     return 0;
 }
 
@@ -1091,6 +1092,7 @@ int UIGrid::set_center(PyUIGridObject* self, PyObject* value, void* closure) {
     }
     self->data->center_x = x;
     self->data->center_y = y;
+    self->data->markDirty(); // #291: camera position change
     return 0;
 }
 
@@ -1186,6 +1188,14 @@ int UIGrid::set_float_member(PyUIGridObject* self, PyObject* value, void* closur
         else if (member_ptr == 7) self->view->camera_rotation = val;
         self->view->position = self->view->box.getPosition();
     }
+
+    // #291: Dirty flag propagation for visual property changes
+    if (member_ptr == 0 || member_ptr == 1) {
+        self->data->markCompositeDirty(); // position change
+    } else {
+        self->data->markDirty(); // content/size change
+    }
+
     return 0;
 }
 // TODO (7DRL Day 2, item 5.) return Texture object
@@ -1310,6 +1320,7 @@ int UIGrid::set_fill_color(PyUIGridObject* self, PyObject* value, void* closure)
     
     PyColorObject* color = (PyColorObject*)value;
     self->data->fill_color = color->data;
+    self->data->markDirty(); // #291: color change
     return 0;
 }
 
@@ -1342,6 +1353,7 @@ int UIGrid::set_perspective(PyUIGridObject* self, PyObject* value, void* closure
     if (value == Py_None) {
         // Clear perspective but keep perspective_enabled unchanged
         self->data->perspective_entity.reset();
+        self->data->markDirty(); // #291: FOV rendering change
         return 0;
     }
     
@@ -1354,6 +1366,7 @@ int UIGrid::set_perspective(PyUIGridObject* self, PyObject* value, void* closure
     PyUIEntityObject* entity_obj = (PyUIEntityObject*)value;
     self->data->perspective_entity = entity_obj->data;
     self->data->perspective_enabled = true;  // Enable perspective when entity assigned
+    self->data->markDirty(); // #291: FOV rendering change
     return 0;
 }
 
@@ -1369,6 +1382,7 @@ int UIGrid::set_perspective_enabled(PyUIGridObject* self, PyObject* value, void*
         return -1;  // Error occurred
     }
     self->data->perspective_enabled = enabled;
+    self->data->markDirty(); // #291: FOV rendering toggle
     return 0;
 }
 
@@ -1401,6 +1415,7 @@ int UIGrid::set_fov(PyUIGridObject* self, PyObject* value, void* closure)
         return -1;
     }
     self->data->fov_algorithm = algo;
+    self->data->markDirty(); // #291: FOV algorithm change
     return 0;
 }
 
@@ -1425,6 +1440,7 @@ int UIGrid::set_fov_radius(PyUIGridObject* self, PyObject* value, void* closure)
         return -1;
     }
     self->data->fov_radius = (int)radius;
+    self->data->markDirty(); // #291: FOV radius change
     return 0;
 }