fix: correct devcontainer workspace path mismatch

Volume was mounting ./backend to /workspaces/backend, but devcontainer.json
pointed VS Code to /workspaces/familienarchiv — causing the broken path shown
in Remote Explorer.

Now mounts the full project root to /workspaces/familienarchiv, which matches
the workspaceFolder variable. Also gives container access to frontend/ for
running npm run generate:api without leaving the devcontainer.

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

docker-compose.yml

@@ -67,7 +67,7 @@ services:
     command: sleep infinity
     restart: unless-stopped
     volumes:
-      - ./backend:/workspaces/backend:cached
+      - .:/workspaces/familienarchiv:cached
       - ./import-data:/import # Mappt den lokalen Ordner "import-data" auf "/import" im Container
     depends_on:
       db: