feat(config): parse effects.windows.shadows from Lua config

Add CfgEffectsWindowShadows struct (12 fields) and CfgEffectsWindows.shadows
member. Add wlr_scene_shadow *shadow field to Client struct for runtime
shadow node tracking. Update example/config.lua with full shadow config
block.

The config parser handles missing shadows table gracefully (all default).

example/config.lua

@@ -59,7 +59,23 @@ monitors = {
 effects = {
 	windows = {
 		rounded = false,
-		rounding = "none",
+		rounding = "none", -- off, light, or heavy
+
+		shadows = {
+			shadows = true,
+			shadow_radius = 24,
+			shadow_offset_x = 0,
+			shadow_offset_y = 8,
+			shadow_color = 0x000000ff,
+			shadow_opacity = 0.30,
+			shadow_expand = 12,
+
+			fullscreen_shadows = false,
+			nogaps_shadows = false,
+			maximized_shadows = false,
+			only_floating = false,
+			shadow_clip = true,
+		},
 	},
 }
 

include/client.h

@@ -14,6 +14,7 @@ struct wlr_layer_surface_v1;
 struct wlr_xdg_surface;
 struct wlr_xwayland_surface;
 struct wlr_xdg_toplevel_decoration_v1;
+struct wlr_scene_shadow;
 
 /* Client types */
 enum { XDGShell, LayerShell, X11 };
@@ -54,6 +55,7 @@ typedef struct Client {
 #endif
 	unsigned int bw;
 	int corner_radius;
+	struct wlr_scene_shadow *shadow;
 	uint32_t tags;
 	int isfloating, isurgent, isfullscreen, isscratchpad;
 	uint32_t resize; /* configure serial of a pending resize */