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/tests/unit/smoke.test.js

@@ -0,0 +1,10 @@
+import { describe, it, expect } from 'vitest';
+
+// Smoke test for the M1-1 harness: proves the JS unit runner works end-to-end.
+// This is deliberately trivial — later cards (M1-2+) replace it with the
+// deterministic-core suite. It must pass to certify the harness is GREEN.
+describe('M1 harness smoke', () => {
+	it('adds numbers (harness is live)', () => {
+		expect(1 + 1).toBe(2);
+	});
+});