fix(docker): Use mirror.gcr.io in all Dockerfiles to avoid rate limits

findagram/frontend/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM node:20-slim AS builder
+FROM mirror.gcr.io/library/node:22-slim AS builder
 
 WORKDIR /app
 
@@ -25,7 +25,7 @@ COPY . .
 RUN npm run build
 
 # Production stage
-FROM nginx:alpine
+FROM mirror.gcr.io/library/nginx:alpine
 
 # Copy built assets from builder stage (CRA outputs to /build)
 COPY --from=builder /app/build /usr/share/nginx/html