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/project.inlang/settings.json

@@ -0,0 +1,16 @@
+{
+	"$schema": "https://inlang.com/schema/project-settings",
+	"modules": [
+		"https://cdn.jsdelivr.net/npm/@inlang/plugin-message-format@4/dist/index.js",
+		"https://cdn.jsdelivr.net/npm/@inlang/plugin-m-function-matcher@2/dist/index.js"
+	],
+	"plugin.inlang.messageFormat": {
+		"pathPattern": "./messages/{locale}.json"
+	},
+	"baseLocale": "en",
+	"locales": [
+		"en",
+		"es",
+		"de"
+	]
+}