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>

iso/docker/entrypoint.sh

@@ -32,6 +32,7 @@ xorg-xrandr
 xorg-xset
 xorg-xsetroot
 xterm
+alacritty
 ttf-dejavu
 ttf-liberation
 noto-fonts
@@ -420,6 +421,59 @@ URxvt*background: #0E1520
 URxvt*foreground: #C8D4E8
 XRES
 
+mkdir -p "$SKEL/.config/alacritty"
+cat > "$SKEL/.config/alacritty/alacritty.toml" <<'ALACRITTY'
+[window]
+padding = { x = 10, y = 8 }
+decorations = "none"
+opacity = 0.96
+title = "Terminal"
+
+[font]
+normal = { family = "DejaVu Sans Mono", style = "Regular" }
+bold   = { family = "DejaVu Sans Mono", style = "Bold" }
+size   = 11.0
+
+[colors.primary]
+background = "#0E1520"
+foreground = "#C8D4E8"
+
+[colors.cursor]
+text   = "#0E1520"
+cursor = "#4A90D9"
+
+[colors.normal]
+black   = "#1A1E2A"
+red     = "#CC4444"
+green   = "#44AA66"
+yellow  = "#BBAA22"
+blue    = "#4488CC"
+magenta = "#8844CC"
+cyan    = "#44AACC"
+white   = "#C8D4E8"
+
+[colors.bright]
+black   = "#3A4050"
+red     = "#FF6666"
+green   = "#66CC88"
+yellow  = "#DDCC44"
+blue    = "#66AAFF"
+magenta = "#AA66FF"
+cyan    = "#66CCEE"
+white   = "#EEF4FF"
+
+[colors.selection]
+background = "#2060A0"
+text       = "#F0F4FF"
+
+[scrolling]
+history = 10000
+
+[cursor]
+style = { shape = "Block", blinking = "On" }
+blink_interval = 500
+ALACRITTY
+
 mkdir -p "$SKEL/.config/dunst"
 cat > "$SKEL/.config/dunst/dunstrc" <<'DUNST'
 [global]