Ensure valid Docker Hub namespace in release workflow

Added validation to normalize input, reject invalid namespaces, and check for proper formatting in the Docker Hub namespace. This prevents configuration mistakes and ensures compliance with naming requirements.

.github/workflows/docker-release.yml

@@ -51,10 +51,28 @@ jobs:
           if [ -z "$NS" ]; then
             NS="${{ secrets.DOCKERHUB_USERNAME }}"
           fi
-          if [ -z "$NS" ]; then
+          
+          # Normalize accidental input like spaces or uppercase.
+          NS="$(echo "$NS" | tr '[:upper:]' '[:lower:]' | xargs)"
+          
+          # Reject clearly invalid placeholders/config mistakes early.
+          if [ -z "$NS" ] || [ "$NS" = "-" ]; then
             echo "Missing Docker Hub namespace. Set repo var DOCKERHUB_NAMESPACE or secret DOCKERHUB_USERNAME."
             exit 1
           fi
+          
+          # Namespace must be a single Docker Hub account/org name, not a path/url.
+          if [[ "$NS" == *"/"* ]] || [[ "$NS" == *":"* ]]; then
+            echo "Invalid Docker Hub namespace '$NS'. Use only the account/org name (e.g. 'nesterovicit')."
+            exit 1
+          fi
+          
+          if ! [[ "$NS" =~ ^[a-z0-9]+([._-][a-z0-9]+)*$ ]]; then
+            echo "Invalid Docker Hub namespace '$NS'. Allowed: lowercase letters, digits, ., _, -"
+            exit 1
+          fi
+          
+          echo "Using Docker Hub namespace: $NS"
           echo "value=$NS" >> "$GITHUB_OUTPUT"
 
       - name: Set up Docker Buildx