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/app.css

@@ -0,0 +1,32 @@
+:root {
+	--bg: #1a1a1a;
+	--fg: #f2f2f2;
+	--accent: #4f9d69;
+	--checker: repeating-conic-gradient(#e8e8e8 0% 25%, #f7f7f7 0% 50%) 0 0 / 24px 24px;
+}
+
+* {
+	box-sizing: border-box;
+}
+
+body {
+	margin: 0;
+	font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
+	background: var(--bg);
+	color: var(--fg);
+}
+
+button {
+	font: inherit;
+	padding: 0.6rem 1rem;
+	border: 0;
+	border-radius: 8px;
+	background: var(--accent);
+	color: #04140b;
+	font-weight: 600;
+	cursor: pointer;
+}
+button:disabled {
+	opacity: 0.5;
+	cursor: not-allowed;
+}

frontend/src/app.html

@@ -0,0 +1,12 @@
+<!doctype html>
+<html lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<link rel="icon" href="%sveltekit.assets%/favicon.png" />
+		<meta name="viewport" content="width=device-width, initial-scale=1" />
+		%sveltekit.head%
+	</head>
+	<body data-sveltekit-preload-data="hover">
+		<div style="display: contents">%sveltekit.body%</div>
+	</body>
+</html>

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>

frontend/src/routes/+page.svelte

@@ -0,0 +1,12 @@
+<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

@@ -0,0 +1,6 @@
+// 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' });
+}