Add command-mode floating switcher overlay

Whenever the command query starts with the existing '>' prefix the shell
now overlays a 640-wide floating panel — backdrop dim, glass card, three
ranked sections (Open tabs from snapshot.tabs, History from
snapshot.history_entries, and a fixed action set for workspace + key
internal routes), and a footer with the design's keyboard hints. Each
result is a real navigation hop; selecting a row dispatches the
appropriate shell action and clears the command query so the overlay
dismisses without leaving stale chrome state.

The overlay reads from the live BrowserSnapshot rather than fabricating
results, and matches case-insensitively against title and URL. Empty
queries surface the most recent items so the panel stays useful even
before the user types.

crates/ely_app/src/shell/render.rs

@@ -7,8 +7,8 @@ use gpui::{
 };
 
 use super::chrome::{
-    PANEL_BG, WallpaperTheme, panel_shadow, render_topbar as render_topbar_chrome,
-    render_wallpaper,
+    PANEL_BG, WallpaperTheme, panel_shadow, render_command_overlay,
+    render_topbar as render_topbar_chrome, render_wallpaper,
 };
 use super::sidebar::collapsed_sidebar_active;
 use super::{ElyShell, ShellState};
@@ -75,6 +75,7 @@ impl ElyShell {
                     .child(self.render_sidebar(&snapshot, sidebar_width, sidebar_collapsed, cx))
                     .child(self.render_main_pane(&snapshot, &active_tab, sidebar_collapsed, cx)),
             )
+            .children(render_command_overlay(&snapshot, cx))
             .into_any_element()
     }