Add a tool to monitor and re-run the client build process

The Javascript ecosystem is rubbish.

flake.nix

@@ -26,6 +26,7 @@
           name = "ld-tools-devshell";
           buildInputs = [
             pkgs.clang
+            pkgs.entr
             pkgs.glade
             pkgs.gtk4
             pkgs.nodejs

music-player/client/package.json

@@ -5,7 +5,8 @@
   "main": "main.js",
   "scripts": {
     "build": "browserify src/main.ts -p [ tsify ] > dist/bundle.js",
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "watch": "exa index.html styles.css src/* | entr -s 'npm run build'"
   },
   "author": "Savanni D'Gerinel <savanni@luminescent-dreams.com>",
   "license": "GPL-3.0-or-later",