refactor: Rename click kwarg to on_click for API consistency (closes #126)

BREAKING CHANGE: Constructor keyword argument renamed from `click` to
`on_click` for all UIDrawable types (Frame, Caption, Sprite, Grid, Line,
Circle, Arc).

Before: Frame(pos=(0,0), size=(100,100), click=handler)
After:  Frame(pos=(0,0), size=(100,100), on_click=handler)

The property name was already `on_click` - this makes the constructor
kwarg match, completing the callback naming standardization from #139.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/UIArc.cpp

@@ -463,7 +463,7 @@ int UIArc::init(PyUIArcObject* self, PyObject* args, PyObject* kwds) {
 
     static const char* kwlist[] = {
         "center", "radius", "start_angle", "end_angle", "color", "thickness",
-        "click", "visible", "opacity", "z_index", "name",
+        "on_click", "visible", "opacity", "z_index", "name",
         nullptr
     };
 
@@ -511,7 +511,7 @@ int UIArc::init(PyUIArcObject* self, PyObject* args, PyObject* kwds) {
     // Handle common UIDrawable properties
     if (click_handler && click_handler != Py_None) {
         if (!PyCallable_Check(click_handler)) {
-            PyErr_SetString(PyExc_TypeError, "click must be callable");
+            PyErr_SetString(PyExc_TypeError, "on_click must be callable");
             return -1;
         }
         self->data->click_register(click_handler);

src/UIArc.h

@@ -134,7 +134,7 @@ namespace mcrfpydef {
             "    color (Color, optional): Arc color. Default: White\n"
             "    thickness (float, optional): Line thickness. Default: 1.0\n\n"
             "Keyword Args:\n"
-            "    click (callable): Click handler. Default: None\n"
+            "    on_click (callable): Click handler. Default: None\n"
             "    visible (bool): Visibility state. Default: True\n"
             "    opacity (float): Opacity (0.0-1.0). Default: 1.0\n"
             "    z_index (int): Rendering order. Default: 0\n"

src/UICaption.cpp

@@ -331,7 +331,7 @@ int UICaption::init(PyUICaptionObject* self, PyObject* args, PyObject* kwds)
     static const char* kwlist[] = {
         "pos", "font", "text",  // Positional args (as per spec)
         // Keyword-only args
-        "fill_color", "outline_color", "outline", "font_size", "click",
+        "fill_color", "outline_color", "outline", "font_size", "on_click",
         "visible", "opacity", "z_index", "name", "x", "y",
         nullptr
     };

src/UICircle.cpp

@@ -400,7 +400,7 @@ PyObject* UICircle::repr(PyUICircleObject* self) {
 int UICircle::init(PyUICircleObject* self, PyObject* args, PyObject* kwds) {
     static const char* kwlist[] = {
         "radius", "center", "fill_color", "outline_color", "outline",
-        "click", "visible", "opacity", "z_index", "name", NULL
+        "on_click", "visible", "opacity", "z_index", "name", NULL
     };
 
     float radius = 10.0f;
@@ -480,7 +480,7 @@ int UICircle::init(PyUICircleObject* self, PyObject* args, PyObject* kwds) {
     // Handle common UIDrawable properties
     if (click_obj && click_obj != Py_None) {
         if (!PyCallable_Check(click_obj)) {
-            PyErr_SetString(PyExc_TypeError, "click must be callable");
+            PyErr_SetString(PyExc_TypeError, "on_click must be callable");
             return -1;
         }
         self->data->click_register(click_obj);

src/UICircle.h

@@ -123,7 +123,7 @@ namespace mcrfpydef {
             "    outline_color (Color, optional): Outline color. Default: Transparent\n"
             "    outline (float, optional): Outline thickness. Default: 0 (no outline)\n\n"
             "Keyword Args:\n"
-            "    click (callable): Click handler. Default: None\n"
+            "    on_click (callable): Click handler. Default: None\n"
             "    visible (bool): Visibility state. Default: True\n"
             "    opacity (float): Opacity (0.0-1.0). Default: 1.0\n"
             "    z_index (int): Rendering order. Default: 0\n"

src/UIFrame.cpp

@@ -504,7 +504,7 @@ int UIFrame::init(PyUIFrameObject* self, PyObject* args, PyObject* kwds)
     static const char* kwlist[] = {
         "pos", "size",  // Positional args (as per spec)
         // Keyword-only args
-        "fill_color", "outline_color", "outline", "children", "click",
+        "fill_color", "outline_color", "outline", "children", "on_click",
         "visible", "opacity", "z_index", "name", "x", "y", "w", "h", "clip_children", "cache_subtree",
         nullptr
     };

src/UIGrid.cpp

@@ -749,7 +749,7 @@ int UIGrid::init(PyUIGridObject* self, PyObject* args, PyObject* kwds) {
     static const char* kwlist[] = {
         "pos", "size", "grid_size", "texture",  // Positional args (as per spec)
         // Keyword-only args
-        "fill_color", "click", "center_x", "center_y", "zoom",
+        "fill_color", "on_click", "center_x", "center_y", "zoom",
         "visible", "opacity", "z_index", "name", "x", "y", "w", "h", "grid_x", "grid_y",
         "layers",  // #150 - layers dict parameter
         nullptr

src/UILine.cpp

@@ -481,7 +481,7 @@ int UILine::init(PyUILineObject* self, PyObject* args, PyObject* kwds) {
 
     static const char* kwlist[] = {
         "start", "end", "thickness", "color",
-        "click", "visible", "opacity", "z_index", "name",
+        "on_click", "visible", "opacity", "z_index", "name",
         nullptr
     };
 
@@ -549,7 +549,7 @@ int UILine::init(PyUILineObject* self, PyObject* args, PyObject* kwds) {
     // Handle click handler
     if (click_handler && click_handler != Py_None) {
         if (!PyCallable_Check(click_handler)) {
-            PyErr_SetString(PyExc_TypeError, "click must be callable");
+            PyErr_SetString(PyExc_TypeError, "on_click must be callable");
             return -1;
         }
         self->data->click_register(click_handler);

src/UILine.h

@@ -119,7 +119,7 @@ namespace mcrfpydef {
             "    thickness (float, optional): Line thickness in pixels. Default: 1.0\n"
             "    color (Color, optional): Line color. Default: White\n\n"
             "Keyword Args:\n"
-            "    click (callable): Click handler. Default: None\n"
+            "    on_click (callable): Click handler. Default: None\n"
             "    visible (bool): Visibility state. Default: True\n"
             "    opacity (float): Opacity (0.0-1.0). Default: 1.0\n"
             "    z_index (int): Rendering order. Default: 0\n"

src/UISprite.cpp

@@ -392,7 +392,7 @@ int UISprite::init(PyUISpriteObject* self, PyObject* args, PyObject* kwds)
     static const char* kwlist[] = {
         "pos", "texture", "sprite_index",  // Positional args (as per spec)
         // Keyword-only args
-        "scale", "scale_x", "scale_y", "click",
+        "scale", "scale_x", "scale_y", "on_click",
         "visible", "opacity", "z_index", "name", "x", "y", "snapshot",
         nullptr
     };