Add real desktop icons plus right-click desktop/icon context menus

Closes "right-click on bare desktop" - previously a true no-op, nothing
rendered above the wallpaper at all. Requested directly: a real desktop
"just like windows does" - Home/Computer/Trash plus one icon per real
~/Desktop entry, individually draggable with persisted grid positions,
double-click to open, right-click menus (per-icon "Open" plus "Set as
Wallpaper" for image files when general.wallpaper_command is set; bare
desktop "New Folder"/"Refresh").

Architecture mirrors the existing context_menu.rs/snap_flyout.rs
"compositor-owned floating UI" pattern: desktop_icons.rs (data model, grid
layout, filesystem scan, hit-test), desktop_icons_state.rs (JSON
persistence, same shape as monitor_layout.rs), desktop_menu.rs (the new
right-click menu, reusing decoration::render_context_menu's existing
rasterizer), state/desktop_icons.rs (CompState glue: rescan/select/drag/
open/persist), and a new decoration::render_desktop_icon rasterizer --
hand-drawn glyphs, since no PNG/SVG decoding capability exists anywhere in
this workspace. Wired into both render loops (udev and winit) above the
wallpaper and below every window, and into input/pointer.rs's button/
motion handlers for selection, drag, double-click, and both menus.

Four new config keys: general.desktop_icons (default true - a directly
requested, purely visual feature, unlike the opt-in-while-experimental
general.gpu), general.file_manager, general.desktop_icon_single_click,
general.wallpaper_command (all default off/empty).

Deliberately out of scope for this pass, stated up front: move-to-trash
and "Empty Trash" (destructive, no confirmation-dialog primitive to gate
them on yet), filesystem watching, multi-select, per-mimetype icon art,
icons on any monitor but the primary one.

124 wayland-crate tests (up from 106), full workspace build and clippy
clean.

2 files changed, 28 insertions, 0 deletions

diff --git a/crates/wayland/src/winit/connect.rs b/crates/wayland/src/winit/connect.rs
index 30eaaf8..227cf33 100644
--- a/crates/wayland/src/winit/connect.rs
+++ b/crates/wayland/src/winit/connect.rs
@@ -151,6 +151,12 @@ impl WaylandPlatform {
             context_menu_buffer: None,
             snap_flyout: None,
             snap_flyout_buffer: None,
+            desktop_icons: None,
+            desktop_icon_buffers: HashMap::new(),
+            desktop_icon_drag: None,
+            desktop_menu: None,
+            desktop_menu_buffer: None,
+            last_icon_click: None,
             wm: wm.clone(),
             surface_to_id: HashMap::new(),
             id_to_window: HashMap::new(),
diff --git a/crates/wayland/src/winit/render.rs b/crates/wayland/src/winit/render.rs
index 345d40c..03fff3d 100644
--- a/crates/wayland/src/winit/render.rs
+++ b/crates/wayland/src/winit/render.rs
@@ -56,6 +56,8 @@ impl WaylandPlatform {
         // trade against silently wrong pixels persisting on screen.
         let age = 0;
         let (renderer, mut framebuffer) = self.backend.bind().map_err(err)?;
+        self.state.ensure_desktop_icons();
+        let desktop_icon_render_list = self.state.desktop_icon_render_list();
 
         // Locked: srdwm's own native lock UI, or an external locker's
         // surface, over an opaque black clear - nothing else, no windows,
@@ -129,6 +131,15 @@ impl WaylandPlatform {
                 Err(e) => log::warn!("failed to import snap flyout buffer: {e}"),
             }
         }
+        // The desktop-icon/bare-desktop right-click menu, if open - same
+        // topmost placement.
+        if let (Some(menu), Some(buffer)) = (self.state.desktop_menu.as_ref(), self.state.desktop_menu_buffer.as_ref()) {
+            let pos = (menu.pos.0 as f64, menu.pos.1 as f64);
+            match MemoryRenderBufferRenderElement::from_buffer(renderer, pos, buffer, None, None, None, Kind::Unspecified) {
+                Ok(elem) => custom_elements.push(crate::rounded_corners::WinitElement::Base(crate::elements::OverlayElement::Memory(elem))),
+                Err(e) => log::warn!("failed to import desktop menu buffer: {e}"),
+            }
+        }
         // Content now renders here too, one window at a time, not through
         // `render_output`'s own `spaces` argument - see this function's
         // own call to `damage_tracker.render_output` further down for why,
@@ -441,6 +452,17 @@ impl WaylandPlatform {
             }
             occluders.push(frame);
         }
+        // Real desktop icons - above the wallpaper, below every window.
+        // See `udev/render.rs`'s matching push site for the full ordering
+        // reasoning; `desktop_icon_render_list` was already captured
+        // right after `self.backend.bind()`, well before this point.
+        for (pos, buffer) in &desktop_icon_render_list {
+            let pos = (pos.0 as f64, pos.1 as f64);
+            match MemoryRenderBufferRenderElement::from_buffer(renderer, pos, buffer, None, None, None, Kind::Unspecified) {
+                Ok(elem) => custom_elements.push(crate::rounded_corners::WinitElement::Base(crate::elements::OverlayElement::Memory(elem))),
+                Err(e) => log::warn!("failed to import desktop icon buffer: {e}"),
+            }
+        }
         // Background/bottom layer-shell (wallpaper engines) last --
         // bottommost, matching smithay's own `space_render_elements`
         // ordering, which this whole custom loop now replaces.