Feat: Add shared ESLint configuration for Upfluence web projects

.gitignore

@@ -0,0 +1 @@
+node_modules

README.md

@@ -75,3 +75,101 @@ export default {
   printWidth: 80 // Override the print width setting
 };
 ```
+
+### ESLint
+
+A shared flat ESLint config (ESLint ≥ 10) for Upfluence Ember apps/addons.
+It includes:
+
+- `eslint:recommended`
+- `eslint-plugin-ember` (+ `emberCompatibilityDisables`)
+- `typescript-eslint` (`recommended`, untyped)
+- `eslint-plugin-qunit` for tests
+- `eslint-plugin-n` for node/config files
+- `eslint-config-prettier`
+
+References:
+
+- [`eslint-phase1-rule-matrix.md`](https://linear.app/upfluence/issue/CD-205/introduce-shared-eslint-configuration#comment-09e0d01c)
+- [`audit.md`](https://linear.app/upfluence/issue/CD-249/w-conf-package-ships-with-a-shared-eslint-config-projectsaddons-can#comment-74f1dbec)
+
+#### Requirements
+
+The ESLint export bundles its plugins and presets as package dependencies.
+In consumer repositories, the minimal install is:
+
+```bash
+pnpm add -D @upfluence/w-conf eslint
+```
+
+#### Legacy Package Removal
+
+When migrating from legacy `.eslintrc`, you can remove:
+
+```bash
+pnpm remove @typescript-eslint/parser @typescript-eslint/eslint-plugin
+```
+
+#### Usage
+
+Create an `eslint.config.mjs` at the root of your project.
+
+By default, the package exports a standard, zero-config resolved array:
+
+```js
+// @ts-check
+import { defineConfig } from 'eslint/config';
+import upfluence from '@upfluence/w-conf/eslint';
+
+export default defineConfig(...upfluence);
+```
+
+To customize globs/ignores, use `buildConfiguration`:
+
+```js
+import { defineConfig } from 'eslint/config';
+import { buildConfiguration } from '@upfluence/w-conf/eslint';
+
+export default defineConfig(
+  ...buildConfiguration({
+    ignores: ['dist/', 'declarations/', 'coverage/', 'my-custom-unlinted-folder/'],
+    testFiles: ['packages/*/tests/**/*-test.{js,ts}'],
+    nodeFiles: ['ember-cli-build.js', 'config/**/*.js', 'gulpfile.js']
+  })
+);
+```
+
+> Unlike the legacy `.eslintrc.js` setup, flat config lints `.ts` files by
+> default — no `--ext` flag needed.
+
+> Note: `.ts` files are linted via `typescript-eslint` with its `recommended`
+> (untyped) preset. Type-aware linting (`recommendedTypeChecked`) is intentionally
+> deferred.
+
+For advanced composition (monorepos, custom blocks), use named exports and keep
+`eslintConfigPrettierPlaceLast` last:
+
+```js
+import { defineConfig } from 'eslint/config';
+import {
+  core,
+  emberConfig,
+  javascript,
+  typescript,
+  qunitTests,
+  nodeFiles,
+  DEFAULT_IGNORES,
+  eslintConfigPrettierPlaceLast
+} from '@upfluence/w-conf/eslint';
+
+export default defineConfig(
+  ...DEFAULT_IGNORES,
+  ...core,
+  ...emberConfig,
+  ...javascript,
+  ...typescript,
+  ...qunitTests(['packages/*/tests/**/*-test.{js,ts}']),
+  ...nodeFiles(),
+  eslintConfigPrettierPlaceLast
+);
+```

package.json

@@ -11,25 +11,43 @@
     "upfluence",
     "configuration",
     "prettier",
+    "eslint",
+    "eslintconfig",
     "shared-config"
   ],
   "publishConfig": {
     "registry": "https://npm.pkg.github.com",
     "access": "public"
   },
+  "engines": {
+    "node": ">=20.0.0"
+  },
   "devDependencies": {
     "@trivago/prettier-plugin-sort-imports": "^5.2.2",
-    "prettier": "^3.6.2"
+    "eslint": "^10.5.0",
+    "prettier": "^3.6.2",
+    "typescript": "^6.0.3"
+  },
+  "dependencies": {
+    "@eslint/js": "^10.0.1",
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-ember": "^13.3.2",
+    "eslint-plugin-n": "^18.1.0",
+    "eslint-plugin-qunit": "^8.2.6",
+    "globals": "^17.7.0",
+    "typescript-eslint": "^8.62.0"
   },
   "peerDependencies": {
     "@trivago/prettier-plugin-sort-imports": "^5.2.2",
+    "eslint": ">=10.5.0",
     "prettier": "^3.6.2"
   },
   "type": "module",
   "files": [
     "src"
   ],
   "exports": {
-    "./prettier": "./src/prettier/index.mjs"
+    "./prettier": "./src/prettier/index.mjs",
+    "./eslint": "./src/eslint/index.mjs"
   }
 }