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

deskbar/include/deskbar.h

@@ -45,10 +45,12 @@
 #define DB_MAX_APPS    32
 
 /* ── per-app context menu ────────────────────────────────────────────── */
-#define DB_CTX_W       140     /* context menu width */
+#define DB_CTX_W       160     /* context menu width */
 #define DB_CTX_ITEM_H   26     /* item row height */
 #define DB_CTX_PAD       4     /* top/bottom padding */
-#define DB_CTX_N         3     /* number of items: Raise, Minimize, Close */
+#define DB_CTX_N         3     /* base items: Raise, Minimize, Close */
+#define DB_CTX_NDESK     4     /* number of "→ Desktop N" items */
+#define DB_CTX_SEP_H     6     /* separator line height */
 
 /* ── fly-out menu ────────────────────────────────────────────────────── */
 #define DB_FLYOUT_W    196     /* fly-out menu panel width */
@@ -102,8 +104,10 @@ static const unsigned long DB_ICON_COLORS[] = {
 typedef struct AppEntry {
     Window win;
     char   title[64];
+    char   cls[64];    /* WM_CLASS instance for icon lookup */
     int    focused;
     int    minimized;
+    int    desktop;    /* which desktop this window is on */
 } AppEntry;
 
 typedef struct Deskbar {