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/src/routes/+layout.svelte

@@ -0,0 +1,13 @@
+<script>
+	import '../app.css';
+</script>
+
+<svelte:head>
+	<title>SlabUploader — Milestone 1</title>
+</svelte:head>
+
+<main>
+	<h1>SlabUploader</h1>
+	<p>Milestone 1 — Capture (browser-only)</p>
+	<slot />
+</main>