Add baseline ESLint config (no boundary rules yet)

.eslintignore

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+dist/
+node_modules/
+ClientApp/
+wwwroot/
+*.cjs
+pnpm-lock.yaml

.eslintrc.cjs

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+/** @type {import('eslint').Linter.Config} */
+module.exports = {
+  root: true,
+  parser: "@typescript-eslint/parser",
+  parserOptions: {
+    ecmaVersion: 2023,
+    sourceType: "module",
+    project: "./tsconfig.json",
+    ecmaFeatures: { jsx: true },
+  },
+  plugins: ["@typescript-eslint", "unused-imports"],
+  extends: [
+    "eslint:recommended",
+    "plugin:@typescript-eslint/recommended",
+  ],
+  rules: {
+    "@typescript-eslint/no-unused-vars": "off",
+    "unused-imports/no-unused-imports": "error",
+    "unused-imports/no-unused-vars": [
+      "warn",
+      {
+        vars: "all",
+        varsIgnorePattern: "^_",
+        args: "after-used",
+        argsIgnorePattern: "^_",
+      },
+    ],
+    "@typescript-eslint/consistent-type-imports": ["error", { prefer: "type-imports" }],
+    "@typescript-eslint/no-explicit-any": "warn",
+    "@typescript-eslint/no-non-null-assertion": "warn",
+    "no-console": ["warn", { allow: ["warn", "error"] }],
+  },
+  ignorePatterns: ["dist/", "node_modules/", "ClientApp/", "wwwroot/", "*.cjs"],
+};

eslint.config.js

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+// 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),
+];