feat: jpeg image rendering, desktop backgrounds, fix memory regression

programs/include/gui/desktop.hpp

@@ -21,10 +21,17 @@ static constexpr int PANEL_HEIGHT = 32;
 struct DesktopSettings {
     // Background
     bool bg_gradient;       // true = gradient, false = solid
+    bool bg_image;          // true = JPEG wallpaper
     Color bg_solid;         // solid background color
     Color bg_grad_top;      // gradient top color
     Color bg_grad_bottom;   // gradient bottom color
 
+    // Wallpaper (valid when bg_image == true)
+    char bg_image_path[128];   // VFS path to current wallpaper
+    uint32_t* bg_wallpaper;    // scaled ARGB pixel buffer (screen-sized)
+    int bg_wallpaper_w;        // scaled width
+    int bg_wallpaper_h;        // scaled height
+
     // Panel
     Color panel_color;      // panel background color
 

programs/include/zenith/heap.h

@@ -39,13 +39,14 @@ namespace heap_detail {
         g_head.next = node;
     }
 
-    static inline void grow(uint64_t bytes) {
+    static inline bool grow(uint64_t bytes) {
         uint64_t pages = (bytes + 0xFFF) / 0x1000;
         if (pages < 4) pages = 4;          // grow at least 16 KiB at a time
 
         void* mem = zenith::alloc(pages * 0x1000);
-        if (mem != nullptr)
-            insert_free(mem, pages * 0x1000);
+        if (mem == nullptr) return false;
+        insert_free(mem, pages * 0x1000);
+        return true;
     }
 
 } // namespace heap_detail
@@ -93,7 +94,8 @@ namespace heap_detail {
         }
 
         // No fit — grow and retry
-        grow(needed);
+        if (!grow(needed))
+            return nullptr;
         return malloc(size);
     }