fix(build): ensure gtk4-layer-shell loads before libwayland-client

- Update CGO_LDFLAGS in build scripts to include gtk4-layer-shell with the correct load order.
- Add a new layershell_link.go file to maintain the dependency on gtk4-layer-shell.
- Modify overlay_gtk.go to clarify the importance of load order for Layer Shell functionality.
- Enhance run.sh to preload gtk4-layer-shell for proper overlay positioning.

src/cmd/captioneer-desktop/layershell_link.go

@@ -0,0 +1,21 @@
+//go:build gtk
+
+package main
+
+/*
+#cgo pkg-config: gtk4-layer-shell-0
+#cgo LDFLAGS: -Wl,--no-as-needed -lgtk4-layer-shell
+
+// gtk4-layer-shell shims libwayland-client. It must appear before
+// libwayland-client in the dynamic loader order or gtk_layer_is_supported()
+// returns false and the overlay becomes an unpositioned normal window.
+// Referencing the symbol from the main package keeps the dependency alive
+// even when the external linker would otherwise drop or reorder it.
+#include <gtk4-layer-shell.h>
+
+static void captioneer_keep_layershell_linked(void) __attribute__((used));
+static void captioneer_keep_layershell_linked(void) {
+	(void)gtk_layer_get_major_version;
+}
+*/
+import "C"

src/output/overlay/overlay_gtk.go

@@ -4,8 +4,9 @@
 package overlay
 
 /*
-#cgo pkg-config: gtk4 gtk4-x11 gtk4-wayland gtk4-layer-shell-0
-#cgo LDFLAGS: -lX11
+#cgo pkg-config: gtk4-layer-shell-0
+#cgo pkg-config: gtk4 gtk4-x11 gtk4-wayland
+#cgo LDFLAGS: -Wl,--no-as-needed -lgtk4-layer-shell -lX11
 
 #include <gtk/gtk.h>
 #include <gtk4-layer-shell.h>
@@ -356,7 +357,7 @@ static CaptioneerOverlay *captioneer_overlay_new(
 		}
 	} else if (wayland) {
 		captioneer_append_warning(warnings,
-			"The Wayland compositor does not support Layer Shell; using a normal window without guaranteed always-on-top, placement, taskbar, or fullscreen behavior.");
+			"Layer Shell is unavailable in this process (often a libwayland load-order problem); using a normal window without guaranteed always-on-top or placement. Try rebuilding so libgtk4-layer-shell loads before libwayland-client, or set overlay backend to x11.");
 	}
 
 	GdkMonitor *size_monitor = overlay->monitor;