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/vite.config.js

@@ -0,0 +1,11 @@
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [sveltekit()],
+	test: {
+		environment: 'node',
+		include: ['tests/unit/**/*.test.js'],
+		exclude: ['tests/e2e/**', 'node_modules/**', 'build/**']
+	}
+});