chore(frontend): drop dead vue-tsc devDep + check script

Frontend is pure JS (no .ts/JSDoc); CI never ran vue-tsc. Removed the devDep and its orphaned `check` script instead of bumping to v3, and updated the ci.yml comment to match.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -10,8 +10,7 @@
     "dev": "vite",
     "build": "vite build",
     "preview": "vite preview",
-    "test:unit": "vitest run",
-    "check": "vue-tsc --noEmit"
+    "test:unit": "vitest run"
   },
   "dependencies": {
     "vue": "^3.4.0",
@@ -23,7 +22,6 @@
   "devDependencies": {
     "@vitejs/plugin-vue": "^6.0.0",
     "vite": "^8.0.0",
-    "vue-tsc": "^2.0.0",
     "vite-plugin-vuetify": "^2.0.0",
     "sass": "^1.71.0",
     "vitest": "^4.0.0",