feat: stage 3 — Vue web UI (dashboard, server page, charts) + docker build ...

Frontend (Vue 3 + Vite, gnexus-ui-kit, chart.js):
- login by admin token (localStorage, Bearer)
- dashboard: server cards with status, CPU/RAM/disk progress, net MB/s, note
- server page: metric cards, info (hostname/os/kernel/ips), editable note,
  history charts (1ч/6ч/24ч/7д), tabs: overview/disks/net/processes/docker
- create-server flow with one-time key display + install command

Backend: serve built SPA from panel/backend/static (assets mount + fallback)

Docker: multi-stage build (node:22 → npm ci/build → static into python image),
build context moved to repo root, .dockerignore added

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