refactor: delegate security to CloudFlare and clean up mailgun-webhook

Remove application-level CORS and IP whitelisting as security is now handled at CloudFlare edge. CORS is not applicable for backend webhook service, and IP whitelisting is more effectively managed at infrastructure layer. Also translate Dockerfile comments to English and add registry URL to build script.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

mailgun-webhook/build-image.sh

@@ -9,18 +9,18 @@ fi
 read -p "BUILD: Push new image to registry [y/n]? " -n 1 -r
 echo    # (optional) move to a new line
 
-PUSH_IMAGE_TO_REPO="$REPLY"
+PUSH_IMAGE="$REPLY"
 
 printf "\nBUILD START ...\n\n"
 
+REGISTRY_URL="registry.budakova.org"
 IMAGE_NAME=$(node -p "require('./package.json').name")
 IMAGE_VERSION=$1
 
-IMAGE_TAG=$IMAGE_NAME:$IMAGE_VERSION
-
+IMAGE_TAG=$REGISTRY_URL/$IMAGE_NAME:$IMAGE_VERSION
 docker build . -t $IMAGE_TAG
 
-if [[ "$PUSH_IMAGE_TO_REPO" =~ ^[Yy]$ ]]
+if [[ "$PUSH_IMAGE" =~ ^[Yy]$ ]]
 then
     printf "\nPushing image ...\n\n"
     docker push $IMAGE_TAG