Revert GHCR mirror configs to Docker Hub direct pulls

Replace ghcr.io/cartsnitch/mirror/* images with Docker Hub originals,
restore GHCR login guard, and add Docker Hub auth.

Refs: CAR-77

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Dockerfile

@@ -1,5 +1,5 @@
 # Stage 1: Build
-FROM ghcr.io/cartsnitch/mirror/node:20-alpine AS build
+FROM node:20-alpine AS build
 
 WORKDIR /app
 
@@ -10,7 +10,7 @@ COPY . .
 RUN npm run build
 
 # Stage 2: Production
-FROM ghcr.io/cartsnitch/mirror/nginx:stable-alpine AS prod
+FROM nginx:stable-alpine AS prod
 
 COPY --from=build /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/conf.d/default.conf