ci: Use self-hosted base images to avoid Docker Hub rate limits

Cached node:20, node:20-slim, and nginx:alpine to code.cannabrands.app.
No more Docker Hub dependency for builds.

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

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

findagram/frontend/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM node:20-slim AS builder
+FROM code.cannabrands.app/creationshop/node:20-slim AS builder
 
 WORKDIR /app
 
@@ -20,7 +20,7 @@ ENV REACT_APP_API_URL=https://cannaiq.co
 RUN npm run build
 
 # Production stage
-FROM nginx:alpine
+FROM code.cannabrands.app/creationshop/nginx:alpine
 
 # Copy built assets from builder stage (CRA outputs to /build)
 COPY --from=builder /app/build /usr/share/nginx/html