feat: English UI, no-login API, logo/favicon, layout fixes ...

- UI fully translated to English (dashboard, server page, toasts, formatters)
- login removed: GHARD_ADMIN_TOKEN is optional now (unset = open API);
  agent key auth untouched; README/.env.example updated
- SVG logo + favicon (monitor with pulse, kit-style)
- reactivity: dashboard poll 5s, server 5s, history 10s
- layout: metric cards full-row flex, metric value nowrap,
  info/note 50/50 grid, topbar logo 48x48, server card max-width 420px,
  uptime on its own line, delete confirmed via GnConfirmDialog
- docker: ca-certificates for npm git dependency

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

feat: stage 1 — panel skeleton (FastAPI + SQLite) and ingest API ...

- FastAPI backend: config (pydantic-settings, GHARD_* env), aiosqlite + WAL
- SQLite schema: servers, metrics, events
- POST /api/v1/ingest: auth by X-Server-Key (sha256 hash), net rates in MB/s
  computed on panel from raw counter deltas, server card upsert
- Servers API: create (key shown once), list with dashboard summary,
  detail, PATCH name/note, delete, metrics history
- Dockerfile + docker-compose with persistent volume

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