fix: run svelte-kit sync before svelte-check in Docker build

.svelte-kit/tsconfig.json is gitignored and must be generated at
build time — svelte-check cannot run without it.

Dockerfile

@@ -5,6 +5,7 @@ RUN corepack enable && corepack prepare pnpm --activate
 COPY frontend/package.json frontend/pnpm-lock.yaml ./
 RUN pnpm install --frozen-lockfile
 COPY frontend/ ./
+RUN pnpm svelte-kit sync
 RUN pnpm run check
 RUN pnpm run build