Fixes #7–#11: launcher Other tab, ICCCM size hints, icon loading, multi-desktop

Fix #7: Add "Other" catch-all category to the launcher. map_category() now
returns "Other" instead of "" for unrecognized .desktop Categories, and an
"Other" tab is added to the CATS list so those apps are discoverable instead
of silently hidden.

Fix #8: Respect ICCCM WM_NORMAL_HINTS. client_add() reads PMinSize,
PResizeInc, and PBaseSize from the window's size hints. The resize drag
handler in events.c clamps to min_w/min_h and snaps to the
width_inc/height_inc grid, fixing jank in character-cell terminal emulators
(xterm, Alacritty).

Fix #10: Optional freedesktop icon loading via imlib2. The launcher now
parses the Icon= field from .desktop files and attempts to render a PNG icon
from Papirus-Dark (or hicolor fallback). When imlib2 is not present the
existing letter-square is shown unchanged. launcher/Makefile auto-detects
imlib2 via pkg-config and sets -DHAVE_IMLIB2.

Fix #11: True 4-desktop support in the WM. Each Client carries a desktop
field (assigned at map time from wm->cur_desktop). Clicking a workspace
button in the deskbar sends _NET_CURRENT_DESKTOP; the WM now handles it via
wm_switch_desktop() which unmaps frames on the leaving desktop, maps frames
on the arriving desktop, and re-focuses. _NET_WM_DESKTOP is set per window
so the deskbar can filter db_update_apps() to show only current-desktop
windows (sticky windows with desktop 0xFFFFFFFF are always shown).

wm/src/client.c

@@ -54,9 +54,12 @@ Client *client_add(WM *wm, Window win) {
     if (client_find_by_win(wm, win))                return NULL;
 
     Client *c = calloc(1, sizeof(Client));
-    c->win = win;
-    c->w   = wa.width;
-    c->h   = wa.height;
+    c->win     = win;
+    c->w       = wa.width;
+    c->h       = wa.height;
+    c->desktop = wm->cur_desktop;
+    c->min_w   = MIN_WIN_W;
+    c->min_h   = MIN_WIN_H;
 
     /* use application-requested position if non-zero, otherwise smart place */
     if (wa.x == 0 && wa.y == 0) {
@@ -93,6 +96,36 @@ Client *client_add(WM *wm, Window win) {
         }
     }
 
+    /* ICCCM WM_NORMAL_HINTS — size constraints and resize increments */
+    {
+        XSizeHints hints;
+        long supplied = 0;
+        if (XGetWMNormalHints(wm->dpy, win, &hints, &supplied)) {
+            if (hints.flags & PMinSize) {
+                if (hints.min_width  > c->min_w) c->min_w = hints.min_width;
+                if (hints.min_height > c->min_h) c->min_h = hints.min_height;
+            }
+            if (hints.flags & PResizeInc) {
+                c->inc_w = hints.width_inc;
+                c->inc_h = hints.height_inc;
+            }
+            if (hints.flags & PBaseSize) {
+                c->base_w = hints.base_width;
+                c->base_h = hints.base_height;
+            } else if (hints.flags & PMinSize) {
+                c->base_w = hints.min_width;
+                c->base_h = hints.min_height;
+            }
+        }
+    }
+
+    /* advertise which desktop this window lives on */
+    {
+        long desk = wm->cur_desktop;
+        XChangeProperty(wm->dpy, win, wm->net_wm_desktop, XA_CARDINAL, 32,
+                        PropModeReplace, (unsigned char *)&desk, 1);
+    }
+
     int fw = (int)c->w + BORDER_W * 2;
     int fh = (int)c->h + TITLE_HEIGHT + BORDER_W;