refactor: register widgets by reference (UiContext::register_host)

register_widget(id, ptr) took a raw pointer in a safe function; cce-ui is
making it an unsafe fn now that every app registers through
register_host(&mut w), which takes the widget's own id and a live borrow.
Registration loops that existed only to hand the registry raw pointers
(and the unsafe blocks and self_ptr casts around them) are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

 src/main.rs | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index e3815e1..15bd41c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -355,11 +355,8 @@ impl Application for TextEditorApp {
         // Widget text comes from the paint walk (Adapted::paint_self serves per-widget fonts).
         if !self.widgets_registered {
             self.widgets_registered = true;
-            let self_ptr = self as *mut Self;
-            unsafe {
-                self.ui_context.register_widget(self.menu_dropdown.base().id(), (*self_ptr).menu_dropdown.as_ptr_mut());
-                self.ui_context.register_widget(self.editor.base().id(), (*self_ptr).editor.as_ptr_mut());
-            }
+            self.ui_context.register_host(&mut self.menu_dropdown);
+            self.ui_context.register_host(&mut self.editor);
         }
 
         if self.initial_focus {