feat: add deployment guide, nginx/systemd configs, switch to adapter-node

- Add docs/DEPLOYMENT.md: step-by-step Proxmox LXC guide (Debian 13,
  PostgreSQL, nginx reverse proxy, systemd services)
- Add nginx/innercontext.conf: proxy /api/ → uvicorn, /mcp/ → uvicorn
  with SSE streaming support, / → SvelteKit Node server
- Add systemd/innercontext.service and innercontext-node.service
- Switch frontend from adapter-auto to adapter-node (required for
  +page.server.ts form actions); install adapter-node 5.5.4
- Update README.md: add frontend, MCP sections; fix /skin-snapshots →
  /skincare; update repo layout
- Replace frontend/README.md generic Svelte template with project docs

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

systemd/innercontext.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=innercontext FastAPI backend
+After=network.target
+
+[Service]
+Type=simple
+User=innercontext
+Group=innercontext
+WorkingDirectory=/opt/innercontext/backend
+EnvironmentFile=/opt/innercontext/backend/.env
+ExecStart=/opt/innercontext/backend/.venv/bin/uvicorn main:app --host 127.0.0.1 --port 8000
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target