feat(clients/windows): WinUI UX batch - tile hover, Settings NavigationView, modal slide-up

Bump windows-reactor + windows to a4f7b2cb (from b4129fcc) for the new
PointerEntered/PointerExited events; migration is mechanical renames only
(SymbolGlyph->Symbol, placeholder->placeholder_text, on_changed->
on_text_changed/on_toggled, on_menu_item_clicked->on_item_clicked,
on_ready->on_mounted). New runtime model: reactor lost its build.rs, so the
client build.rs stages the WinAppSDK bootstrap via
windows-reactor-setup::as_framework_dependent() and main calls
windows_reactor::bootstrap() (missing either = 0x80040154 at launch);
staged filenames unchanged, so pack-msix and the MSIX manifest are untouched.

- Host tiles: WinUI pointer-over fill (ControlFillSecondary) via the new
  pointer enter/exit events, hover id in root state (backend-wired handlers
  bypass the reconciler flush, like the flyout clicks).
- Settings: stock NavigationView sidebar (Windows-Settings pattern) with
  Display/Video/Input/Audio/About panes, built-in back arrow, wide content
  column, and a per-section content slide-up tween. The section card is
  KEYED by section: an in-place diff across sections re-sets a reused
  ComboBox's items (clearing WinUI's selection) but skips selected_index
  when the values compare equal, rendering a blank selection - the key
  forces a remount. Card titles/descriptions dropped; per-control guidance
  moved to hover tooltips (ToolTipService).
- New "Show the stats overlay (HUD)" setting (show_hud, default on),
  honored mid-stream via the 400 ms HUD re-render.
- Add-host modal: entrance fade + slide-up tween (scrim fades with it).
- Self-initiated disconnect (Ctrl+Alt+Shift+D -> Ended(None)) returns to
  the host list silently instead of raising the error banner.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/windows/src/app/pair.rs

@@ -26,7 +26,7 @@ pub(crate) fn pair_page(props: &Svc, cx: &mut RenderCx) -> Element {
         );
         button("Pair & Connect")
             .accent()
-            .icon(SymbolGlyph::Accept)
+            .icon(Symbol::Accept)
             .on_click(move || {
                 let pin = code2.trim().to_string();
                 let (ctx3, ss, st, target3) =
@@ -65,7 +65,7 @@ pub(crate) fn pair_page(props: &Svc, cx: &mut RenderCx) -> Element {
     let cancel_btn = {
         let ss = set_screen.clone();
         button("Cancel")
-            .icon(SymbolGlyph::Cancel)
+            .icon(Symbol::Cancel)
             .on_click(move || ss.call(Screen::Hosts))
     };
     // The no-PIN alternative offered alongside the PIN ceremony: open an identified connect that
@@ -73,7 +73,7 @@ pub(crate) fn pair_page(props: &Svc, cx: &mut RenderCx) -> Element {
     let request_btn = {
         let (svc, target2) = (props.clone(), target.clone());
         button("Request access without a PIN")
-            .icon(SymbolGlyph::Send)
+            .icon(Symbol::Send)
             .on_click(move || request_access(&svc, &target2))
             .horizontal_alignment(HorizontalAlignment::Stretch)
     };
@@ -105,9 +105,9 @@ pub(crate) fn pair_page(props: &Svc, cx: &mut RenderCx) -> Element {
             .informational()
             .is_closable(false),
         text_box(code)
-            .placeholder("PIN")
+            .placeholder_text("PIN")
             .font_size(28.0)
-            .on_changed(move |s| set_code.call(s)),
+            .on_text_changed(move |s| set_code.call(s)),
         hstack((pair_btn, cancel_btn)).spacing(8.0),
         text_block(
             "Don\u{2019}t have a PIN? Request access instead and approve this device on the host \