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>

wm/src/events.c

@@ -66,6 +66,10 @@ void on_expose(WM *wm, XExposeEvent *e) {
         menu_draw(wm);
         return;
     }
+    if (wm->swl_visible && e->window == wm->swl_win) {
+        switcher_draw(wm);
+        return;
+    }
     Client *c = client_find_by_frame(wm, e->window);
     if (c && !c->minimized) frame_draw(wm, c);
 }
@@ -259,13 +263,17 @@ void on_key_press(WM *wm, XKeyEvent *e) {
     if ((e->state & Mod1Mask) && sym == XK_F4 && wm->focused)
         send_delete(wm, wm->focused->win);
 
-    /* Alt+Tab — cycle windows */
-    if ((e->state & Mod1Mask) && sym == XK_Tab && wm->clients) {
-        Client *start = wm->focused ? wm->focused->next : wm->clients;
-        Client *n = start;
-        while (n && n->minimized) n = n->next;
-        if (!n) { n = wm->clients; while (n && n->minimized) n = n->next; }
-        if (n && n != wm->focused) client_focus(wm, n);
+    /* Alt+Tab — visual switcher */
+    if ((e->state & Mod1Mask) && sym == XK_Tab) {
+        if (wm->swl_visible) switcher_next(wm);
+        else if (wm->clients) switcher_show(wm);
+        return;
+    }
+
+    /* While switcher is visible, eat all other keys until Alt released */
+    if (wm->swl_visible) {
+        if (sym == XK_Escape) switcher_hide(wm, 0);
+        return;
     }
 
     /* Alt+F9 — minimize */
@@ -300,3 +308,11 @@ void on_key_press(WM *wm, XKeyEvent *e) {
     if (sym == XK_Escape && wm->menu_visible)
         menu_hide(wm);
 }
+
+void on_key_release(WM *wm, XKeyEvent *e) {
+    if (!wm->swl_visible) return;
+    KeySym sym = XLookupKeysym(e, 0);
+    if (sym == XK_Alt_L || sym == XK_Alt_R ||
+        sym == XK_Meta_L || sym == XK_Meta_R)
+        switcher_hide(wm, 1);
+}