Switch to pre-built Docker Hub image for production

- Push app image to jpscott84/drinktracker on Docker Hub
- docker-compose.prod.yml uses image instead of build
- install.sh pulls image instead of building from source
- Much faster deploys (no npm ci/build on target server)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

install.sh

@@ -293,13 +293,13 @@ ENVEOF
   success "$ENV_FILE created (permissions: 600)"
 fi
 
-# ─── Step 5: Build & Start ──────────────────────────────────
+# ─── Step 5: Pull & Start ────────────────────────────────────
 
 echo ""
-info "Building Docker images (this may take a few minutes on first run)..."
+info "Pulling Docker images..."
 echo ""
 
-dc build --no-cache
+dc pull
 
 echo ""
 info "Starting services..."
@@ -398,7 +398,7 @@ echo -e "  ${BOLD}Useful commands:${NC}"
 echo "    View logs:     $DC_CMD logs -f"
 echo "    Stop:          $DC_CMD down"
 echo "    Restart:       $DC_CMD restart"
-echo "    Rebuild:       $DC_CMD up -d --build"
+echo "    Update:        $DC_CMD pull && $DC_CMD up -d"
 echo ""
 echo -e "  ${BOLD}${YELLOW}Next steps:${NC}"
 echo "    1. Open ${APP_URL_CHECK} and create your account"