chore: move homepage override and icon cache to $BASE_DIR/data, add migration code

migrations/utils.go

@@ -0,0 +1,16 @@
+package migrations
+
+import (
+	"os"
+	"path/filepath"
+)
+
+func mv(old, new string) error {
+	if _, err := os.Stat(old); os.IsNotExist(err) {
+		return nil
+	}
+	if err := os.MkdirAll(filepath.Dir(new), 0o755); err != nil {
+		return err
+	}
+	return os.Rename(old, new)
+}