Add clean script

build.mjs

···
 const watch = process.argv.includes("--watch");
 const browser = process.argv.includes("--browser");
 const mv2 = process.argv.includes("--mv2");
+const clean = process.argv.includes("--clean");
 
 const buildBranch = process.env.MOONLIGHT_BRANCH ?? "dev";
 const buildVersion = process.env.MOONLIGHT_VERSION ?? "dev";
···
 
 const promises = [];
 
-if (browser) {
+if (clean) {
+  fs.rmSync("./dist", { recursive: true, force: true });
+} else if (browser) {
   build("browser", "packages/browser/src/index.ts");
 } else {
   for (const [name, entry] of Object.entries(config)) {

package.json

···
   "scripts": {
     "build": "node build.mjs",
     "dev": "node build.mjs --watch",
+    "clean": "node build.mjs --clean",
     "browser": "node build.mjs --browser",
     "browser-mv2": "node build.mjs --browser --mv2",
     "lint": "eslint packages",