Clean Flutter build cache before CI build

.gitea/workflows/build-and-deploy.yml

@@ -22,6 +22,13 @@ jobs:
           auth="$(printf '%s:%s' "${{ secrets.REGISTRY_USERNAME }}" "${{ secrets.REGISTRY_TOKEN }}" | base64 | tr -d '\n')"
           printf '{"auths":{"gitea.dsrptlab.com":{"auth":"%s"}}}\n' "$auth" > ~/.docker/config.json
 
+      - name: Free Docker build space
+        run: |
+          set -euo pipefail
+          docker buildx prune --all --force || true
+          docker builder prune --all --force || true
+          docker system prune --all --force || true
+
       - name: Build and push image
         run: |
           set -euo pipefail