restructure: flatten workspace nesting, move devcontainer to root

- backend/workspaces/backend/ → backend/
- backend/workspaces/frontend/ → frontend/
- backend/.devcontainer/ + .vscode/ → repo root (where VS Code expects them)
- loose scripts/SQL files → scripts/
- replace nested git repo with single repo at project root
- update docker-compose.yml build context and devcontainer.json path
- add root .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/page.svelte.spec.ts

@@ -0,0 +1,13 @@
+import { page } from 'vitest/browser';
+import { describe, expect, it } from 'vitest';
+import { render } from 'vitest-browser-svelte';
+import Page from './+page.svelte';
+
+describe('/+page.svelte', () => {
+	it('should render h1', async () => {
+		render(Page);
+		
+		const heading = page.getByRole('heading', { level: 1 });
+		await expect.element(heading).toBeInTheDocument();
+	});
+});