feat : add ESLint linter to frontend with pre-commit hook

Add ESLint with @nuxt/eslint-config enforcing 4-space indentation.
Add make nuxt-lint and nuxt-lint-fix targets.
Add ESLint check to pre-commit hook (lint only, no auto-fix).
Fix auth.vue indentation from 2 to 4 spaces.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -8,7 +8,9 @@
     "generate": "nuxt generate",
     "preview": "nuxt preview",
     "postinstall": "nuxt prepare",
-    "build:dist": "nuxt generate && rm -rf dist && cp -R .output/public dist"
+    "build:dist": "nuxt generate && rm -rf dist && cp -R .output/public dist",
+    "lint": "eslint .",
+    "lint:fix": "eslint . --fix"
   },
   "dependencies": {
     "@malio/layer-ui": "^1.2.3",
@@ -21,5 +23,13 @@
     "pinia": "^3.0.4",
     "vue": "^3.5.29",
     "vue-router": "^4.6.4"
+  },
+  "devDependencies": {
+    "@nuxt/eslint-config": "^1.9.0",
+    "@typescript-eslint/eslint-plugin": "^8.44.1",
+    "@typescript-eslint/parser": "^8.44.1",
+    "eslint": "^9.36.0",
+    "eslint-plugin-vue": "^10.5.0",
+    "vue-eslint-parser": "^10.2.0"
   }
 }