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;
+}