test: add ESLint and Vitest configuration

- Add ESLint with TypeScript support for linting
- Add Vitest for unit testing
- Add lint and test npm scripts
- Fix lint warnings in ManifestEditorProvider and ValidationService
- Add basic test file to verify setup

Author: CalvinAllen

.eslintrc.json

@@ -0,0 +1,43 @@
+{
+  "root": true,
+  "parser": "@typescript-eslint/parser",
+  "parserOptions": {
+    "ecmaVersion": 2022,
+    "sourceType": "module"
+  },
+  "plugins": [
+    "@typescript-eslint"
+  ],
+  "extends": [
+    "eslint:recommended",
+    "plugin:@typescript-eslint/recommended"
+  ],
+  "rules": {
+    "@typescript-eslint/naming-convention": [
+      "warn",
+      {
+        "selector": "import",
+        "format": ["camelCase", "PascalCase"]
+      }
+    ],
+    "@typescript-eslint/no-unused-vars": [
+      "warn",
+      {
+        "argsIgnorePattern": "^_",
+        "varsIgnorePattern": "^_"
+      }
+    ],
+    "@typescript-eslint/no-explicit-any": "warn",
+    "no-case-declarations": "off",
+    "curly": "warn",
+    "eqeqeq": "warn",
+    "no-throw-literal": "warn",
+    "semi": "warn"
+  },
+  "ignorePatterns": [
+    "out",
+    "node_modules",
+    "webview-ui",
+    "**/*.test.ts"
+  ]
+}