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

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+<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>

frontend/src/routes/+page.svelte

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+<script>
+	/** M1 placeholder home — the 5-state capture flow is built in later cards. */
+</script>
+
+<div class="capture">
+	<h2>Capture</h2>
+	<p>The M1 capture flow (Add photo → Mask → Length axis → Measure → PNG) lands in cards M1-3…M1-5.</p>
+</div>
+
+<style>
+	.capture { max-width: 720px; margin: 2rem auto; padding: 0 1rem; }
+</style>

frontend/src/routes/api/health/+server.js

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+// Minimal health route so the UAT container has a non-SPA probe target.
+import { json } from '@sveltejs/kit';
+
+export function GET() {
+	return json({ ok: true, milestone: 1, app: 'slab-uploader' });
+}