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, 126 insertions, 0 deletions

diff --git a/crates/wayland/src/desktop_menu.rs b/crates/wayland/src/desktop_menu.rs
new file mode 100644
index 0000000..810e639
--- /dev/null
+++ b/crates/wayland/src/desktop_menu.rs
@@ -0,0 +1,126 @@
+//! Right-click desktop icon / bare-desktop menu - the sibling of
+//! `context_menu.rs`'s titlebar window menu, same shape (own `open`/`row_
+//! at`, rasterized via `decoration::render_context_menu`), for the two new
+//! right-click targets desktop icons add: an icon itself, or bare desktop.
+
+use crate::desktop_icons::{DesktopIcon, IconKind};
+
+#[derive(Clone)]
+pub(crate) enum DesktopMenuAction {
+    /// Open the icon with this id - same action a double-click runs.
+    OpenIcon(String),
+    /// Shell out to `general.wallpaper_command` with this icon's path --
+    /// only ever offered for an image-file icon, and only when that
+    /// config key is actually set (see `WindowManager::wallpaper_command`'s
+    /// own doc comment).
+    SetWallpaper(String),
+    NewFolder,
+    Refresh,
+}
+
+pub(crate) struct DesktopMenu {
+    pub(crate) pos: (i32, i32),
+    pub(crate) width: u32,
+    pub(crate) row_height: u32,
+    pub(crate) items: Vec<(&'static str, DesktopMenuAction)>,
+}
+
+const MENU_WIDTH: u32 = 170;
+const ROW_HEIGHT: u32 = 28;
+
+/// Extensions `render_desktop_icon`'s `IconKind::File` icons treat as an
+/// image for "Set as Wallpaper" purposes - not a real mimetype sniff (no
+/// such capability exists anywhere in this workspace, see `desktop_icons.
+/// rs`'s own doc comment on why icon art itself is hand-drawn, not
+/// decoded), just the common raster formats a wallpaper tool actually
+/// accepts.
+const IMAGE_EXTENSIONS: &[&str] = &["png", "jpg", "jpeg", "webp", "bmp", "gif"];
+
+fn is_image_path(path: &std::path::Path) -> bool {
+    path.extension().and_then(|e| e.to_str()).map(|e| IMAGE_EXTENSIONS.iter().any(|ext| e.eq_ignore_ascii_case(ext))).unwrap_or(false)
+}
+
+impl DesktopMenu {
+    /// Right-click on `icon` itself: "Open" always, plus "Set as Wallpaper"
+    /// when `icon` is an image file and `wallpaper_command` is non-empty.
+    pub(crate) fn open_for_icon(icon: &DesktopIcon, pos: (i32, i32), wallpaper_command: &str) -> Self {
+        let mut items = vec![("Open", DesktopMenuAction::OpenIcon(icon.id.clone()))];
+        if icon.kind == IconKind::File && !wallpaper_command.is_empty() && is_image_path(&icon.target) {
+            items.push(("Set as Wallpaper", DesktopMenuAction::SetWallpaper(icon.id.clone())));
+        }
+        Self { pos, width: MENU_WIDTH, row_height: ROW_HEIGHT, items }
+    }
+
+    /// Right-click on bare desktop (no icon under the pointer): "New
+    /// Folder" and "Refresh".
+    pub(crate) fn open_for_desktop(pos: (i32, i32)) -> Self {
+        let items = vec![("New Folder", DesktopMenuAction::NewFolder), ("Refresh", DesktopMenuAction::Refresh)];
+        Self { pos, width: MENU_WIDTH, row_height: ROW_HEIGHT, items }
+    }
+
+    pub(crate) fn height(&self) -> i32 {
+        self.row_height as i32 * self.items.len() as i32
+    }
+
+    /// Same shape as `ContextMenu::row_at`.
+    pub(crate) fn row_at(&self, x: i32, y: i32) -> Option<usize> {
+        if x < self.pos.0 || x >= self.pos.0 + self.width as i32 {
+            return None;
+        }
+        let rel_y = y - self.pos.1;
+        if rel_y < 0 || rel_y >= self.height() {
+            return None;
+        }
+        Some((rel_y / self.row_height as i32) as usize)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    fn icon(kind: IconKind, target: &str) -> DesktopIcon {
+        DesktopIcon { id: "x".into(), label: "x".into(), kind, target: PathBuf::from(target), cell: (0, 0), selected: false }
+    }
+
+    #[test]
+    fn image_file_with_a_configured_command_gets_the_wallpaper_row() {
+        let menu = DesktopMenu::open_for_icon(&icon(IconKind::File, "pic.png"), (0, 0), "swww img");
+        assert_eq!(menu.items.len(), 2);
+        assert_eq!(menu.items[1].0, "Set as Wallpaper");
+    }
+
+    #[test]
+    fn image_file_with_no_configured_command_has_no_wallpaper_row() {
+        let menu = DesktopMenu::open_for_icon(&icon(IconKind::File, "pic.png"), (0, 0), "");
+        assert_eq!(menu.items.len(), 1, "Open only");
+    }
+
+    #[test]
+    fn non_image_file_has_no_wallpaper_row_even_with_a_command_configured() {
+        let menu = DesktopMenu::open_for_icon(&icon(IconKind::File, "notes.txt"), (0, 0), "swww img");
+        assert_eq!(menu.items.len(), 1, "Open only");
+    }
+
+    #[test]
+    fn a_folder_never_gets_the_wallpaper_row() {
+        let menu = DesktopMenu::open_for_icon(&icon(IconKind::Folder, "pic.png"), (0, 0), "swww img");
+        assert_eq!(menu.items.len(), 1, "a directory named like an image is still not a file");
+    }
+
+    #[test]
+    fn desktop_menu_offers_new_folder_and_refresh() {
+        let menu = DesktopMenu::open_for_desktop((10, 10));
+        assert_eq!(menu.items[0].0, "New Folder");
+        assert_eq!(menu.items[1].0, "Refresh");
+    }
+
+    #[test]
+    fn row_at_maps_a_point_to_the_right_row() {
+        let menu = DesktopMenu::open_for_desktop((100, 100));
+        assert_eq!(menu.row_at(150, 100), Some(0));
+        assert_eq!(menu.row_at(150, 100 + ROW_HEIGHT as i32), Some(1));
+        assert_eq!(menu.row_at(150, 100 + menu.height()), None, "just below the menu");
+    }
+}