fix: Use public Docker Hub images instead of private registry

Switch FROM directives to use public Docker Hub images:
- node:20-slim (instead of git.spdy.io/creationshop/node:20-slim)
- nginx:alpine (instead of git.spdy.io/creationshop/nginx:alpine)

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

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

backend/Dockerfile

@@ -1,6 +1,6 @@
 # Build stage
 # Image: git.spdy.io/creationshop/dispensary-scraper
-FROM git.spdy.io/creationshop/node:20-slim AS builder
+FROM node:20-slim AS builder
 
 # Install build tools for native modules (bcrypt, sharp)
 RUN apt-get update && apt-get install -y \
@@ -27,7 +27,7 @@ RUN npm run build
 RUN npm prune --production
 
 # Production stage
-FROM git.spdy.io/creationshop/node:20-slim
+FROM node:20-slim
 
 # Build arguments for version info
 ARG APP_BUILD_VERSION=dev