core: migrate to dankgo shared go modules, embed quickshell in DMS

binary to mount at runtime, -c or DMS_SHELL_DIR overrides required to
explicitly override embedded configuration

core/internal/shellembed/shellembed.go

@@ -0,0 +1,36 @@
+// Package shellembed carries the quickshell UI inside the dms binary and
+// materializes it at runtime via dankgo/shellapp/shellfs, since quickshell
+// needs a real filesystem path. Customization goes through -c /
+// DMS_SHELL_DIR instead of editing the extraction.
+package shellembed
+
+import (
+	"io/fs"
+	"path"
+
+	"github.com/AvengeMedia/dankgo/shellapp/shellfs"
+)
+
+const (
+	distRoot   = "dist"
+	shellEntry = "shell.qml"
+)
+
+// Available reports whether this binary was built with the embedded UI
+// (the withshell build tag).
+func Available() bool {
+	info, err := fs.Stat(distFS, path.Join(distRoot, shellEntry))
+	return err == nil && !info.IsDir()
+}
+
+func Extract(baseDir string) (string, error) {
+	sub, err := fs.Sub(distFS, distRoot)
+	if err != nil {
+		return "", err
+	}
+	return shellfs.Extract(sub, baseDir)
+}
+
+func Prune(baseDir, keep string) {
+	shellfs.Prune(baseDir, keep)
+}