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 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index d638274..8df41eb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -413,9 +413,9 @@ impl State {
         // Root Container DISSOLVED (Phase 6ax): the card and the session list are the two
         // dispatch/walk roots; register them directly (link_parent_child used to do it as a
         // side effect of the root links).
-        ctx.register_widget(self.bg.id(), self.bg.as_ptr_mut());
-        ctx.register_widget(self.card.id(), self.card.as_ptr_mut());
-        ctx.register_widget(self.session_list.id(), self.session_list.as_ptr_mut());
+        ctx.register_host(&mut self.bg);
+        ctx.register_host(&mut self.card);
+        ctx.register_host(&mut self.session_list);
         focus::link_parent_child(&mut self.card, &mut self.username_box, ctx);
         focus::link_parent_child(&mut self.card, &mut self.password_box, ctx);
         focus::link_parent_child(&mut self.card, &mut self.login_btn, ctx);