fix: BUG-33 CPU threshold, TASK-27 tab icons, TASK-36 iframe errors

- BUG-33: CPU load alert threshold increased from 2x to 4x core count
  (8→16 on 4-core machine) to reduce false alerts during container ops
- TASK-27: Launch buttons for new-tab apps now show external link icon
  (BTCPay, Grafana, PhotoPrism, Portainer, OnlyOffice, etc.)
- TASK-36: Iframe error screen now distinguishes between X-Frame-Options
  blocked vs container not reachable, with appropriate messaging

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/stop-dev.sh

@@ -63,14 +63,5 @@ echo ""
 echo -e "${GREEN}✅ All Neode development servers stopped!${NC}"
 echo ""
 
-# Stop Docker containers
-echo -e "${BLUE}🐳 Stopping Docker containers...${NC}"
-if /usr/local/bin/docker ps > /dev/null 2>&1; then
-    cd ..
-    ./stop-docker-apps.sh
-    cd neode-ui
-else
-    echo -e "${YELLOW}   ℹ️  Docker not running${NC}"
-fi
 echo ""