ci/cd: remove backend build step and update frontend subproject to dirty state

.env

@@ -1 +0,0 @@
-VITE_BACKEND_DOMAIN=https://api.snusxd.site

.gitea/workflows/deploy.yml

@@ -11,13 +11,8 @@ jobs:
         with:
           submodules: true
 
-      - name: docker build backend
-        working-directory: ./backend
-        run: docker build -t mva-backend:latest .
-
-      # - name: docker build frontend
-      #   working-directory: ./frontend
-      #   run: docker build -t mva-frontend:latest .
-
       - name: docker compose
         run: docker compose up -d --build
+
+      - name: cleanup old images
+        run: docker image prune -f