refactor: hold widgets in Owned boxes (cce-ui Owned<W>)

The UiContext registry keeps raw pointers to registered widgets, and a
widget that moved while registered (its Vec reallocating, its struct
returned by value) left one pointing at the old address. Each widget
field is now an Owned<Adapted<..>> — a heap box whose allocation, not the
widget, carries the liveness token the registry watches — so the
registered address never moves and is dropped from the registry when the
box is freed. Field access is unchanged through Deref; construction
sites wrap in Owned::new.

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

 src/main.rs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 2094739..dde7822 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -33,6 +33,7 @@ use std::path::{Path, PathBuf};
 use std::sync::OnceLock;
 use std::time::{Duration, Instant};
 
+use cce_ui::widget::Owned;
 use cce_ui::engine::{Application, CursorIcon, EngineState, LogicalPosition, LogicalSize, WindowSettings};
 use cce_ui::scene::layout::Rect;
 use cce_ui::scene::paint::{DisplayList, PaintCtx};
@@ -234,10 +235,10 @@ struct NotesApp {
     hist_pos: usize,
 
     switcher: Option<Switcher>,
-    switcher_input: Adapted<TextBox>,
+    switcher_input: Owned<Adapted<TextBox>>,
 
     left_tab: LeftTab,
-    search_input: Adapted<TextBox>,
+    search_input: Owned<Adapted<TextBox>>,
     search_panel: Panel,
     /// The query the search panel shows results for.
     search_seen: String,
@@ -1634,9 +1635,9 @@ impl Application for NotesApp {
             history: Vec::new(),
             hist_pos: 0,
             switcher: None,
-            switcher_input,
+            switcher_input: Owned::new(switcher_input),
             left_tab: LeftTab::Files,
-            search_input,
+            search_input: Owned::new(search_input),
             search_panel: Panel::default(),
             search_seen: String::new(),
             show_side: true,