Add baseline ESLint config (no boundary rules yet)

eslint.config.js

@@ -0,0 +1,37 @@
+// ESLint v9 flat-config shim that loads the legacy `.eslintrc.cjs` via FlatCompat.
+// The plan (`docs/superpowers/plans/2026-04-14-phase-1a1-skeleton.md`, Task 4)
+// specifies `.eslintrc.cjs` verbatim, but ESLint v9 requires a flat config file
+// to be present. This shim preserves the plan's rule set without modifying
+// package.json's `lint` script. A future batch can migrate fully to flat config.
+
+import { FlatCompat } from "@eslint/eslintrc";
+import js from "@eslint/js";
+import { createRequire } from "node:module";
+import { fileURLToPath } from "node:url";
+import path from "node:path";
+
+const require = createRequire(import.meta.url);
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+const legacyConfig = require("./.eslintrc.cjs");
+
+const compat = new FlatCompat({
+  baseDirectory: __dirname,
+  resolvePluginsRelativeTo: __dirname,
+  recommendedConfig: js.configs.recommended,
+});
+
+export default [
+  {
+    ignores: [
+      "dist/",
+      "node_modules/",
+      "ClientApp/",
+      "wwwroot/",
+      "**/*.cjs",
+      "pnpm-lock.yaml",
+    ],
+  },
+  ...compat.config(legacyConfig),
+];