macOS-style polish: fix seam, bidirectional Alt+Tab, minimized windows in switcher, rounded corners, deskbar context menu

Fix #1: Replace hardcoded 185px deskbar-offset in client.c and events.c with
DESKBAR_W constant (200) to eliminate the 15px gap between the WM frame and
deskbar edge.

Fix #2: Add Shift+Alt+Tab reverse-direction support — grab Mod1+Shift+XK_Tab
in wm.c, detect ShiftMask in events.c, and implement switcher_prev() in
switcher.c.

Fix #3: Include minimized windows in the Alt+Tab switcher. swl_populate() no
longer skips minimized clients; swl_mini[] tracks state so switcher_draw()
can dim them with bracketed titles and darker card backgrounds.

Fix #4: Rewrite themes/picom.conf with macOS-inspired settings — 10px corner
radius on normal windows, 8px on menus, soft downward shadow (radius 18,
offset-y 8, opacity 0.35), smooth fading (step 0.08), no dock/tray rounding.

Fix #5: Add per-app right-click context menu to the deskbar. Right-clicking
an app row opens a popup with Raise / Minimize / Close actions (Close shown
in red). Actions are sent as EWMH client messages (_NET_ACTIVE_WINDOW,
WM_CHANGE_STATE+IconicState, _NET_CLOSE_WINDOW) with matching handlers added
to the WM's on_client_message. Pointer grab closes the menu on any outside
click.

wm/src/events.c

@@ -33,7 +33,7 @@ static void check_snap(WM *wm, Client *c) {
         } else {
             client_snap_left(wm, c);
         }
-    } else if (c->x + (int)(c->w + BORDER_W * 2) >= sw - 185 - SNAP_DIST) {
+    } else if (c->x + (int)(c->w + BORDER_W * 2) >= sw - DESKBAR_W - SNAP_DIST) {
         client_snap_right(wm, c);
     } else if (c->y <= SNAP_DIST) {
         client_maximize(wm, c);
@@ -95,10 +95,34 @@ void on_enter_notify(WM *wm, XCrossingEvent *e) {
 }
 
 void on_client_message(WM *wm, XClientMessageEvent *e) {
-    Atom net_active = XInternAtom(wm->dpy, "_NET_ACTIVE_WINDOW", False);
+    Atom net_active       = XInternAtom(wm->dpy, "_NET_ACTIVE_WINDOW",  False);
+    Atom net_close        = XInternAtom(wm->dpy, "_NET_CLOSE_WINDOW",   False);
+    Atom wm_change_state  = XInternAtom(wm->dpy, "WM_CHANGE_STATE",     False);
+
     if (e->message_type == net_active) {
         Client *c = client_find_by_win(wm, e->window);
         if (c) client_restore(wm, c);
+        return;
+    }
+    if (e->message_type == net_close) {
+        Client *c = client_find_by_win(wm, e->window);
+        if (c) {
+            XEvent ev = {0};
+            ev.xclient.type         = ClientMessage;
+            ev.xclient.window       = c->win;
+            ev.xclient.message_type = wm->wm_protocols;
+            ev.xclient.format       = 32;
+            ev.xclient.data.l[0]    = wm->wm_delete_window;
+            ev.xclient.data.l[1]    = CurrentTime;
+            XSendEvent(wm->dpy, c->win, False, NoEventMask, &ev);
+        }
+        return;
+    }
+    /* WM_CHANGE_STATE IconicState → minimize */
+    if (e->message_type == wm_change_state && e->data.l[0] == 3) {
+        Client *c = client_find_by_win(wm, e->window);
+        if (c && !c->minimized) client_minimize(wm, c);
+        return;
     }
 }
 
@@ -263,10 +287,19 @@ 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 — visual switcher */
+    /* Alt+Tab / Shift+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);
+        int backward = (e->state & ShiftMask) != 0;
+        if (wm->swl_visible) {
+            if (backward) switcher_prev(wm);
+            else          switcher_next(wm);
+        } else if (wm->clients) {
+            switcher_show(wm);
+            if (backward && wm->swl_visible) {
+                wm->swl_idx = wm->swl_count - 1;
+                switcher_draw(wm);
+            }
+        }
         return;
     }