Queue AlphaClaw and OpenClaw installs across restarts

[chrysb]

Summary

• queue AlphaClaw self-updates and OpenClaw updates behind pending markers, then apply them with a real npm install during boot instead of copy-merging node_modules
• wait for the AlphaClaw process to come back before closing the AlphaClaw update modal or reloading after an OpenClaw update, and show Restarting... while that handoff is in progress
• add targeted server and frontend coverage for the pending install helpers, restart polling, and update routes

Testing

• npm test -- tests/server/openclaw-version.test.js tests/server/pending-openclaw-update.test.js tests/server/routes-system.test.js tests/frontend/api.test.js tests/server/alphaclaw-version.test.js tests/server/pending-alphaclaw-update.test.js tests/frontend/update-modal-helpers.test.js tests/bin/alphaclaw.test.js
• npm run build:ui