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/README.md

@@ -0,0 +1,38 @@
+# sv
+
+Everything you need to build a Svelte project, powered by [`sv`](https://github.com/sveltejs/cli).
+
+## Creating a project
+
+If you're seeing this, you've probably already done this step. Congrats!
+
+```sh
+# create a new project in the current directory
+npx sv create
+
+# create a new project in my-app
+npx sv create my-app
+```
+
+## Developing
+
+Once you've created a project and installed dependencies with `npm install` (or `pnpm install` or `yarn`), start a development server:
+
+```sh
+npm run dev
+
+# or start the server and open the app in a new browser tab
+npm run dev -- --open
+```
+
+## Building
+
+To create a production version of your app:
+
+```sh
+npm run build
+```
+
+You can preview the production build with `npm run preview`.
+
+> To deploy your app, you may need to install an [adapter](https://svelte.dev/docs/kit/adapters) for your target environment.