build: add the npm toolchain with ESLint, JSDoc and node --test

@tauri-apps/cli is a local devDependency. ESLint runs the recommended
and JSDoc rules, with browser globals for ui/ and node globals for tests
and scripts. npm test runs node --test over tests/js.

eslint.config.js

@@ -0,0 +1,26 @@
+import js from '@eslint/js';
+import jsdoc from 'eslint-plugin-jsdoc';
+import globals from 'globals';
+
+export default [
+  {
+    ignores: ['target/', 'gen/', 'node_modules/'],
+  },
+  js.configs.recommended,
+  jsdoc.configs['flat/recommended-error'],
+  {
+    files: ['ui/**/*.js'],
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        __TAURI__: 'readonly',
+      },
+    },
+  },
+  {
+    files: ['tests/**/*.js', 'scripts/**/*.js', 'eslint.config.js'],
+    languageOptions: {
+      globals: globals.node,
+    },
+  },
+];

package.json

@@ -0,0 +1,19 @@
+{
+  "name": "claude-code-usage-bubble",
+  "private": true,
+  "description": "Floating bubble showing Claude Code and Codex usage",
+  "license": "Apache-2.0",
+  "type": "module",
+  "scripts": {
+    "tauri": "tauri",
+    "lint": "eslint .",
+    "test": "node --test \"tests/js/**/*.test.js\""
+  },
+  "devDependencies": {
+    "@eslint/js": "^10.0.1",
+    "@tauri-apps/cli": "^2.12.3",
+    "eslint": "^10.13.0",
+    "eslint-plugin-jsdoc": "^65.4.0",
+    "globals": "^17.13.0"
+  }
+}