Add ESLint to the frontend

Wires up @nuxt/eslint (the official Nuxt module) so `npm run lint`,
already documented in CLAUDE.md's pre-completion checklist, actually
exists. It auto-generates a flat config aware of Nuxt's auto-imports,
so it doesn't flag composables and utils that Nuxt injects without an
explicit import.

frontend/package.json

@@ -8,7 +8,8 @@
     "generate": "nuxt generate",
     "preview": "nuxt preview",
     "postinstall": "nuxt prepare",
-    "typecheck": "nuxt typecheck"
+    "typecheck": "nuxt typecheck",
+    "lint": "eslint ."
   },
   "dependencies": {
     "marked": "^18.0.11",
@@ -18,6 +19,8 @@
     "vue-router": "^5.2.0"
   },
   "devDependencies": {
+    "@nuxt/eslint": "^1.17.0",
+    "eslint": "^10.10.0",
     "typescript": "^5.9.3",
     "vue-tsc": "^3.3.11"
   }