Add Sidebar / Layout cards to appearance form

Below the appearance rows the Appearance form now exposes the design's
"Sidebar / Layout" section: serif "Layout" sub-headline plus a 2-up
preview-card grid wired to the active space's sidebar_width — Single
column lands on DEFAULT_SIDEBAR_WIDTH_PX, Compact lands on
COLLAPSED_SIDEBAR_WIDTH_PX. Each card draws a miniature sidebar +
canvas preview so the choice reads at a glance.

The shell exposes a new set_active_sidebar_width helper alongside the
existing toggle so the cards mutate state without re-implementing the
toggle logic. The "Hidden on hover" preset from the design is omitted
until that mode actually ships — no placeholder option.

The cards live in chrome::appearance_layout_cards so appearance_form
stays under 500 lines.

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

@@ -8,6 +8,8 @@ use gpui::{
 };
 use gpui_component::{IconName, scroll::ScrollableElement};
 
+use super::appearance_layout_cards::render_sidebar_layout_section;
+
 use crate::shell::ElyShell;
 use crate::shell::chrome::SERIF_FAMILY;
 
@@ -31,7 +33,8 @@ pub(crate) fn render_appearance_form(
                 .gap(px(28.0))
                 .child(render_header())
                 .child(render_wallpaper_grid(snapshot, cx))
-                .child(render_appearance_rows(snapshot, cx)),
+                .child(render_appearance_rows(snapshot, cx))
+                .child(render_sidebar_layout_section(snapshot, cx)),
         )
         .into_any_element()
 }

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

@@ -0,0 +1,163 @@
+use ely_browser_core::BrowserSnapshot;
+use ely_design_system::colors;
+use ely_domain::{COLLAPSED_SIDEBAR_WIDTH_PX, DEFAULT_SIDEBAR_WIDTH_PX};
+use gpui::{
+    AnyElement, Context, FontWeight, InteractiveElement, IntoElement, ParentElement, SharedString,
+    StatefulInteractiveElement, Styled, div, prelude::FluentBuilder, px, rgb, rgba,
+};
+
+use crate::shell::ElyShell;
+use crate::shell::chrome::SERIF_FAMILY;
+
+pub(crate) fn render_sidebar_layout_section(
+    snapshot: &BrowserSnapshot,
+    cx: &mut Context<ElyShell>,
+) -> AnyElement {
+    let active_width = snapshot
+        .spaces
+        .iter()
+        .find(|space| space.id() == &snapshot.active_space_id)
+        .map(|space| space.sidebar_width_px())
+        .unwrap_or(DEFAULT_SIDEBAR_WIDTH_PX);
+    let compact = active_width <= COLLAPSED_SIDEBAR_WIDTH_PX;
+
+    div()
+        .flex()
+        .flex_col()
+        .gap(px(14.0))
+        .pt(px(8.0))
+        .child(
+            div()
+                .text_size(px(11.0))
+                .text_color(rgb(colors::INK_4))
+                .child("SIDEBAR"),
+        )
+        .child(
+            div()
+                .font_family(SERIF_FAMILY)
+                .text_size(px(22.0))
+                .font_weight(FontWeight(400.0))
+                .text_color(rgb(colors::INK))
+                .child("Layout"),
+        )
+        .child(
+            div()
+                .grid()
+                .grid_cols(2)
+                .gap(px(10.0))
+                .child(render_layout_card(
+                    "Single column",
+                    "Default · workspace + tabs.",
+                    !compact,
+                    LayoutMode::Single,
+                    cx,
+                ))
+                .child(render_layout_card(
+                    "Compact",
+                    "Icons-only with launcher rail.",
+                    compact,
+                    LayoutMode::Compact,
+                    cx,
+                )),
+        )
+        .into_any_element()
+}
+
+#[derive(Clone, Copy)]
+enum LayoutMode {
+    Single,
+    Compact,
+}
+
+fn render_layout_card(
+    title: &'static str,
+    detail: &'static str,
+    selected: bool,
+    mode: LayoutMode,
+    cx: &mut Context<ElyShell>,
+) -> AnyElement {
+    let id = SharedString::from(match mode {
+        LayoutMode::Single => "layout-single",
+        LayoutMode::Compact => "layout-compact",
+    });
+
+    div()
+        .id(id)
+        .p(px(14.0))
+        .rounded(px(14.0))
+        .bg(rgba(LAYOUT_CARD_BG))
+        .when(selected, |el| el.border_2().border_color(rgb(colors::ACCENT)))
+        .when(!selected, |el| el.border_1().border_color(rgba(colors::STROKE)))
+        .flex()
+        .flex_col()
+        .gap(px(10.0))
+        .cursor_pointer()
+        .hover(|style| style.opacity(0.94))
+        .active(|style| style.opacity(0.85))
+        .on_click(cx.listener(move |shell, _, _, cx| {
+            let width = match mode {
+                LayoutMode::Single => DEFAULT_SIDEBAR_WIDTH_PX,
+                LayoutMode::Compact => COLLAPSED_SIDEBAR_WIDTH_PX,
+            };
+            shell.set_active_sidebar_width(width, cx);
+        }))
+        .child(render_layout_preview(mode))
+        .child(
+            div()
+                .flex()
+                .flex_col()
+                .gap(px(2.0))
+                .child(
+                    div()
+                        .text_size(px(12.5))
+                        .font_weight(FontWeight(500.0))
+                        .text_color(rgb(colors::INK))
+                        .child(title),
+                )
+                .child(
+                    div()
+                        .text_size(px(11.0))
+                        .text_color(rgb(colors::INK_4))
+                        .child(detail),
+                ),
+        )
+        .into_any_element()
+}
+
+fn render_layout_preview(mode: LayoutMode) -> AnyElement {
+    let sidebar_width = match mode {
+        LayoutMode::Single => 56.0,
+        LayoutMode::Compact => 18.0,
+    };
+
+    div()
+        .h(px(96.0))
+        .rounded(px(8.0))
+        .bg(rgb(0xffffff))
+        .relative()
+        .child(
+            div()
+                .absolute()
+                .left(px(6.0))
+                .top(px(6.0))
+                .bottom(px(6.0))
+                .w(px(sidebar_width))
+                .rounded(px(5.0))
+                .bg(rgba(LAYOUT_PANEL_BG)),
+        )
+        .child(
+            div()
+                .absolute()
+                .left(px(sidebar_width + 12.0))
+                .top(px(6.0))
+                .right(px(6.0))
+                .bottom(px(6.0))
+                .rounded(px(5.0))
+                .bg(rgba(LAYOUT_CANVAS_BG)),
+        )
+        .into_any_element()
+}
+
+const LAYOUT_CARD_BG: u32 = 0xffffffd9;
+const LAYOUT_PANEL_BG: u32 = 0x281e1414;
+const LAYOUT_CANVAS_BG: u32 = 0x281e140a;

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

@@ -1,4 +1,5 @@
 pub(crate) mod appearance_form;
+pub(crate) mod appearance_layout_cards;
 pub(crate) mod brand_glyph;
 pub(crate) mod command_footer;
 pub(crate) mod command_overlay;

crates/ely_app/src/shell/sidebar.rs

@@ -112,6 +112,20 @@ impl ElyShell {
         }
     }
 
+    pub(crate) fn set_active_sidebar_width(&mut self, width_px: u16, cx: &mut Context<Self>) {
+        let ShellState::Ready(core) = &mut self.state else {
+            return;
+        };
+        let active_space_id = match core.snapshot() {
+            Ok(snapshot) => snapshot.active_space_id,
+            Err(_) => return,
+        };
+
+        if core.set_space_sidebar_width(&active_space_id, width_px).is_ok() {
+            cx.notify();
+        }
+    }
+
     fn render_compact_space_button(
         &mut self,
         index: usize,