Phase 1: Alt+Tab switcher, dark GTK theme, alacritty terminal

- Alt+Tab now shows a centered visual switcher overlay with window cards;
  cycling with Tab, committing on Alt release, cancelling with Escape
- GTK3 and GTK2 themes rewritten in dark navy palette matching skywm/
  skydeskbar color constants (was an off-brand tan/BeOS palette)
- Add alacritty to ISO packages with pre-configured dark color scheme;
  update all menu Terminal entries to launch alacritty instead of xterm
- Add KeyReleaseMask to WM root event selection to detect Alt release

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

deskbar/src/deskbar.c

@@ -453,7 +453,7 @@ static const char *S0_LBL[] = {
     "Media Player","Image Viewer","OnlyOffice","PDF Viewer"
 };
 static const char *S0_CMD[] = {
-    "firefox &","xterm &","thunar &","mousepad &",
+    "firefox &","alacritty &","thunar &","mousepad &",
     "mpv --player-operation-mode=pseudo-gui &","viewnior &",
     "onlyoffice-desktopeditors &","evince &"
 };
@@ -471,12 +471,12 @@ static const char *S1_CMD[] = {
 #define NS1 5
 
 static const MI MENU[] = {
-    { "Install SkyOS...", "xterm -e 'sudo skyinstall; exec bash' &", 0, 0,-1 },
+    { "Install SkyOS...", "alacritty -e bash -c 'sudo skyinstall; exec bash' &", 0, 0,-1 },
     { NULL,               NULL,                                       1, 0,-1 },
     { "Applications",     NULL,                                       0, 1, 0 },
     { "Settings",         NULL,                                       0, 1, 1 },
     { NULL,               NULL,                                       1, 0,-1 },
-    { "About SkyOS",      "xterm -e 'fastfetch; read' &",            0, 0,-1 },
+    { "About SkyOS",      "alacritty -e bash -c 'fastfetch; read' &", 0, 0,-1 },
     { "Lock Screen",      "xscreensaver-command -lock &",             0, 0,-1 },
     { NULL,               NULL,                                       1, 0,-1 },
     { "Restart",          "systemctl reboot",                         0, 0,-1 },