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.

scripts/distrobox/build.sh

@@ -19,6 +19,9 @@ build_script='set -Eeuo pipefail
 repo_root=$1
 shift
 cd -- "$repo_root"
+# gtk4-layer-shell must precede libwayland-client in the loader order or the
+# Wayland shim never installs and the overlay cannot be positioned.
+export CGO_LDFLAGS="-Wl,--no-as-needed -lgtk4-layer-shell ${CGO_LDFLAGS:-}"
 go build "$@" -o build/captioneer ./src/cmd/captioneer
 go build "$@" -tags gtk -o build/captioneer-desktop ./src/cmd/captioneer-desktop'