fix: migrate VS Code extension to ESLint 9 flat config

ESLint ^9.x dropped support for .eslintrc.json and the --ext flag.
npm run lint would fail on CI.

- Create eslint.config.mjs (flat config format)
- Add typescript-eslint and @eslint/js dependencies
- Update lint script: remove --ext ts flag
- Delete legacy .eslintrc.json

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: vicperdana

packages/vscode-extension/.eslintrc.json

@@ -0,0 +1,20 @@
+// @ts-check
+import eslint from "@eslint/js";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+    eslint.configs.recommended,
+    ...tseslint.configs.recommended,
+    {
+        files: ["src/**/*.ts"],
+        rules: {
+            "@typescript-eslint/naming-convention": "warn",
+            "curly": "warn",
+            "eqeqeq": "warn",
+            "no-throw-literal": "warn",
+        },
+    },
+    {
+        ignores: ["out/", "dist/", "**/*.d.ts"],
+    }
+);

packages/vscode-extension/eslint.config.mjs

@@ -60,7 +60,7 @@
     "compile": "tsc -p ./",
     "watch": "tsc -watch -p ./",
     "pretest": "npm run compile",
-    "lint": "eslint src --ext ts",
+    "lint": "eslint src",
     "test": "node ./out/test/runTest.js",
     "pack": "vsce package",
     "publish": "vsce publish",
@@ -85,7 +85,9 @@
     "glob": "^11.1.0",
     "mocha": "^11.1.0",
     "typescript": "^5.4.5",
-    "vscode-test": "^1.6.1"
+    "vscode-test": "^1.6.1",
+    "typescript-eslint": "^8.45.0",
+    "@eslint/js": "^9.28.0"
   },
   "dependencies": {
     "@vscode/vsce": "^3.3.2"