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/connect.rs

@@ -270,7 +270,9 @@ fn connect_with(
                 break;
             }
             SessionEvent::Ended(err) => {
-                st.call(err.unwrap_or_else(|| "Session ended".into()));
+                // `None` = the user ended the session themselves (the disconnect shortcut) —
+                // return to the host list silently; an error banner would read as a failure.
+                st.call(err.unwrap_or_default());
                 gamepad.detach();
                 ss.call(Screen::Hosts);
                 break;
@@ -343,7 +345,7 @@ pub(crate) fn request_access_page(
     let cancel_btn = {
         let (ctx, ss) = (ctx.clone(), set_screen.clone());
         button("Cancel")
-            .icon(SymbolGlyph::Cancel)
+            .icon(Symbol::Cancel)
             .on_click(move || {
                 // Return the UI immediately; the parked connect is blocking with no abort, so trip
                 // the flag this request's event loop captured — it then tears down silently when