fix(ci): use internal registry for node:20-alpine base image

- Change FROM node:20-alpine to FROM registry.nxtgauge.com/node:20-alpine
- Update both Dockerfile and Dockerfile.simple
- Fixes Docker Hub rate limiting errors in Woodpecker builds

Images to mirror:
- docker pull node:20-alpine
- docker tag node:20-alpine registry.nxtgauge.com/node:20-alpine
- docker push registry.nxtgauge.com/node:20-alpine

Dockerfile

@@ -29,7 +29,7 @@ ENV NODE_OPTIONS="--max-old-space-size=4096"
 RUN npm run build
 
 # Runtime stage
-FROM node:20-alpine
+FROM registry.nxtgauge.com/node:20-alpine
 WORKDIR /app
 
 # Copy built output

Dockerfile.simple

@@ -1,4 +1,4 @@
-FROM node:20-alpine
+FROM registry.nxtgauge.com/node:20-alpine
 
 WORKDIR /app