Replace sidebar header with workspace picker row

The design's sidebar opens with an ELY title row plus a three-part
workspace picker: a layout-grid tile (opens spaces settings), a glass
pill showing the active space's emoji + name (cycles to next space on
click), and a plus button (opens spaces settings). The previous header
was a static title + space-name label that did not match the design.

Cycle behaviour reuses the existing select_next_space core API to avoid
introducing a new state flow; the existing SelectNextSpace shortcut
delegates through the same helper.

crates/ely_app/src/shell/chrome/mod.rs

@@ -1,3 +1,5 @@
+pub(crate) mod sidebar_header;
 pub(crate) mod wallpaper;
 
+pub(crate) use sidebar_header::render_sidebar_header;
 pub(crate) use wallpaper::{WallpaperTheme, render_wallpaper};