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/events.c

@@ -94,11 +94,55 @@ void on_enter_notify(WM *wm, XCrossingEvent *e) {
     if (c && !c->minimized) set_cursor(wm, c, e->x, e->y);
 }
 
+static void wm_switch_desktop(WM *wm, int new_desk) {
+    if (new_desk < 0 || new_desk >= 4 || new_desk == wm->cur_desktop) return;
+
+    /* hide windows on old desktop */
+    for (Client *c = wm->clients; c; c = c->next) {
+        if (!c->minimized && c->desktop == wm->cur_desktop)
+            XUnmapWindow(wm->dpy, c->frame);
+    }
+
+    wm->cur_desktop = new_desk;
+
+    /* show windows on new desktop */
+    for (Client *c = wm->clients; c; c = c->next) {
+        if (!c->minimized && c->desktop == new_desk)
+            XMapWindow(wm->dpy, c->frame);
+    }
+
+    /* update focus */
+    if (wm->focused && wm->focused->desktop != new_desk) {
+        wm->focused->focused = 0;
+        frame_draw(wm, wm->focused);
+        wm->focused = NULL;
+    }
+    if (!wm->focused) {
+        for (Client *c = wm->clients; c; c = c->next) {
+            if (!c->minimized && c->desktop == new_desk) {
+                client_focus(wm, c);
+                break;
+            }
+        }
+    }
+
+    /* advertise new desktop */
+    long nd = new_desk;
+    XChangeProperty(wm->dpy, wm->root, wm->net_current_desktop, XA_CARDINAL, 32,
+                    PropModeReplace, (unsigned char *)&nd, 1);
+}
+
 void on_client_message(WM *wm, XClientMessageEvent *e) {
     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);
 
+    /* _NET_CURRENT_DESKTOP → switch virtual desktop */
+    if (e->message_type == wm->net_current_desktop && e->window == wm->root) {
+        wm_switch_desktop(wm, (int)e->data.l[0]);
+        return;
+    }
+
     if (e->message_type == net_active) {
         Client *c = client_find_by_win(wm, e->window);
         if (c) client_restore(wm, c);
@@ -271,8 +315,18 @@ void on_motion_notify(WM *wm, XMotionEvent *e) {
     } else {
         int nw = (int)wm->drag_win_w + dx;
         int nh = (int)wm->drag_win_h + dy;
-        if (nw < MIN_WIN_W) nw = MIN_WIN_W;
-        if (nh < MIN_WIN_H) nh = MIN_WIN_H;
+        /* clamp to minimum */
+        if (nw < c->min_w) nw = c->min_w;
+        if (nh < c->min_h) nh = c->min_h;
+        /* snap to resize-increment grid (e.g. terminal character cells) */
+        if (c->inc_w > 1) {
+            nw = c->base_w + ((nw - c->base_w) / c->inc_w) * c->inc_w;
+            if (nw < c->min_w) nw += c->inc_w;
+        }
+        if (c->inc_h > 1) {
+            nh = c->base_h + ((nh - c->base_h) / c->inc_h) * c->inc_h;
+            if (nh < c->min_h) nh += c->inc_h;
+        }
         c->w = (unsigned)nw; c->h = (unsigned)nh;
         XResizeWindow(wm->dpy, c->frame, c->w+BORDER_W*2, c->h+TITLE_HEIGHT+BORDER_W);
         XResizeWindow(wm->dpy, c->win, c->w, c->h);