feat(m1-1): scaffold SvelteKit + Dockerfile + TDD test harness

- SvelteKit (JS, adapter-node) home page + /api/health route
- frontend/Dockerfile multi-stage build->serve (slabuploader-m1:local, 349MB)
- Test harness: Vitest unit + Playwright e2e; smoke tests RED->GREEN verified
- Build, image build, and image serve all verified

frontend/Dockerfile

@@ -0,0 +1,18 @@
+# SlabUploader M1 — frontend only (no FastAPI/Woo). Multi-stage: build then serve.
+FROM node:22-alpine AS build
+WORKDIR /app
+COPY package*.json ./
+RUN npm install
+COPY . .
+RUN npm run build
+
+FROM node:22-alpine AS run
+WORKDIR /app
+ENV NODE_ENV=production
+COPY package*.json ./
+RUN npm install --omit=dev
+COPY --from=build /app/build ./build
+COPY --from=build /app/node_modules ./node_modules
+EXPOSE 80
+ENV PORT=80
+CMD ["node", "build/index.js"]