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/app.d.ts

@@ -0,0 +1,25 @@
+// src/app.d.ts
+
+declare global {
+	namespace App {
+		// Define the User structure matching your Java Entity
+		interface User {
+			id: string;
+			username: string;
+			groups: {
+				name: string;
+				permissions: string[];
+			}[];
+		}
+
+		interface Locals {
+			user?: User; // locals.user is optional (undefined if not logged in)
+		}
+
+		interface PageData {
+			user?: User; // Available in $page.data.user
+		}
+	}
+}
+
+export {};