Fix Unexpected Keyword in MediaManager and Add Build Linting

- Fix corrupted line in src/MediaManager.html causing syntax error.
- Add ESLint integration to build process to prevent future syntax errors.
- Create .eslintrc.js with TypeScript and HTML support.
- Relax strict lint rules to accommodate existing codebase.

package.json

@@ -6,7 +6,8 @@
     "global.ts"
   ],
   "scripts": {
-    "build": "webpack --mode production",
+    "build": "npm run lint && webpack --mode production",
+    "lint": "eslint \"src/**/*.{ts,js,html}\"",
     "deploy": "clasp push",
     "test": "jest",
     "test:log": "jest > test_output.txt 2>&1",
@@ -15,7 +16,11 @@
   "devDependencies": {
     "@types/google-apps-script": "^1.0.85",
     "@types/jest": "^30.0.0",
+    "@typescript-eslint/eslint-plugin": "^7.18.0",
+    "@typescript-eslint/parser": "^7.18.0",
     "copy-webpack-plugin": "^13.0.1",
+    "eslint": "^8.57.1",
+    "eslint-plugin-html": "^8.1.3",
     "gas-webpack-plugin": "^2.6.0",
     "graphql-tag": "^2.12.6",
     "husky": "^9.1.7",