Add 6 desktop features: workspace shortcuts, Exposé, deskbar icons, notifications, screen lock, move-to-desktop

- Super+1-4: switch virtual desktop; Super+Shift+1-4: move focused window to desktop N
- Super+Space: Exposé window overview (tiled grid), click to select, Escape to cancel
- wm/src/expose.c: expose_show/expose_hide using ceil(sqrt) grid layout with saved/restored geometry
- client_move_to_desktop(): moves window between desktops, fires _NET_WM_DESKTOP update
- on_client_message: handles _NET_WM_DESKTOP to move windows from external requests
- deskbar: optional imlib2 app icon rendering (Papirus-Dark → Papirus → hicolor → pixmaps fallback)
- deskbar: XGetClassHint populates cls field for better icon lookup
- deskbar: context menu extended with separator + "→ Desktop 1-4" items via _NET_WM_DESKTOP
- orionnotify/: freedesktop.org notification daemon (libdbus-1), stacks up to 5 popups top-right
- orionlock/: PAM-authenticated fullscreen screen lock with clock, date, password dots
- Lock Screen menu item wired to orionlock
- Root Makefile includes orionnotify and orionlock targets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GHiBQKPfUoaJgCKuA9op1H

wm/src/client.c

@@ -328,6 +328,34 @@ void client_snap_left(WM *wm, Client *c) {
     frame_draw(wm, c);
 }
 
+void client_move_to_desktop(WM *wm, Client *c, int new_desk) {
+    if (new_desk < 0 || new_desk >= 4 || c->desktop == new_desk) return;
+
+    /* hide frame if it's on the current (now-active) desktop */
+    if (c->desktop == wm->cur_desktop && !c->minimized)
+        XUnmapWindow(wm->dpy, c->frame);
+
+    c->desktop = new_desk;
+
+    /* update _NET_WM_DESKTOP */
+    long desk = new_desk;
+    XChangeProperty(wm->dpy, c->win, wm->net_wm_desktop, XA_CARDINAL, 32,
+                    PropModeReplace, (unsigned char *)&desk, 1);
+
+    /* if we moved the focused window away, re-focus another */
+    if (wm->focused == c) {
+        wm->focused->focused = 0;
+        frame_draw(wm, wm->focused);
+        wm->focused = NULL;
+        for (Client *n = wm->clients; n; n = n->next) {
+            if (!n->minimized && n->desktop == wm->cur_desktop) {
+                client_focus(wm, n);
+                break;
+            }
+        }
+    }
+}
+
 void client_snap_right(WM *wm, Client *c) {
     if (c->maximized) client_unmaximize(wm, c);
     int sw = DisplayWidth(wm->dpy, wm->screen);