Typescript: API Modules > Enforce TypeScript checks in CI

### Follow-up: enforce TypeScript checks in CI

**Problem:** nothing type-checks `.ts` in CI today, so the types added across Phase 3 aren't verified anywhere. `build` compiles via `ts-loader` with `transpileOnly` (won't fail on type errors), and the `lint` script globs only `.js`/`.vue`. The per-PR `vue-tsc --noEmit` checks and the per-directory `strict: true` rollout are therefore advisory only — a `.ts` type regression passes CI today (e.g. the existing `composables/services/MqttExpertTopicHelper.ts` error that nothing catches).

**Tasks:**
- [ ] Add a `typecheck` script to `package.json`: `vue-tsc --noEmit`
- [ ] Add a CI step running `typecheck` — start **non-blocking** (the pre-existing `MqttExpertTopicHelper.ts` error would otherwise make it red), then make it required once that's resolved
- [ ] Extend the `lint` script glob to include `frontend/**/*.ts`