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.

1 files changed, 16 insertions, 0 deletions

diff --git a/crates/config/src/engine/support.rs b/crates/config/src/engine/support.rs
index 9f7e537..76fbe62 100644
--- a/crates/config/src/engine/support.rs
+++ b/crates/config/src/engine/support.rs
@@ -154,6 +154,22 @@ pub(super) fn default_config() -> HashMap<String, ConfigValue> {
     // every other ordinary flag rather than left absent for a backend to
     // decide.
     set("general.gpu", Bool(false));
+    // Real desktop icons (Home/Computer/Trash plus `~/Desktop`'s own
+    // contents) on by default - see `WindowManager::desktop_icons_
+    // enabled`'s own doc comment for why this, unlike `general.gpu` just
+    // above, doesn't need an opt-in safety net.
+    set("general.desktop_icons", Bool(true));
+    // Empty by default - see `WindowManager::file_manager`'s own doc
+    // comment: empty means "dispatch via `xdg-open`", not "no file manager
+    // configured, do nothing".
+    set("general.file_manager", String(std::string::String::new()));
+    // Double-click by default - see `WindowManager::desktop_icon_single_
+    // click`'s own doc comment.
+    set("general.desktop_icon_single_click", Bool(false));
+    // Empty by default - see `WindowManager::wallpaper_command`'s own doc
+    // comment: empty means "Set as Wallpaper" doesn't appear at all, not
+    // "configured to do nothing".
+    set("general.wallpaper_command", String(std::string::String::new()));
     // Deliberately *not* seeded here, unlike every other `general.*` key --
     // its actual default differs by backend (GLES/winit: on; udev/Pixman:
     // off, an untested-on-real-hardware CPU cost too real to default to on