Add FastPanel deployment guide

docs/FASTPANEL.md

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+# FastPanel-safe frontend deployment
+
+The VPS runs FastPanel, so deployment must update only project static files and must not manage the whole web stack.
+
+## FastPanel sites
+
+Create these sites in FastPanel:
+
+- `admin.example.ru`
+- `widget.example.ru`
+- `api.example.ru`
+
+The admin and widget domains should serve static files.
+
+## Safe deploy user
+
+Create a limited deploy user or run deploys as the FastPanel site owner. The user needs write access only to:
+
+```text
+/opt/raspi-chat/source
+/var/www/<fastpanel-user>/data/www/admin.example.ru
+/var/www/<fastpanel-user>/data/www/widget.example.ru
+```
+
+## What the deploy script does
+
+```text
+git fetch/pull
+npm ci
+build admin-panel
+build widget
+rsync dist files into FastPanel web roots
+```
+
+## What the deploy script must not do
+
+```text
+edit /etc/nginx/nginx.conf
+rewrite FastPanel vhost configs
+restart nginx/apache/mysql/php-fpm
+bind to ports 80/443
+remove /var/www parent directories
+```
+
+## Environment
+
+Copy:
+
+```bash
+cp deploy/deploy-agent/.env.example deploy/deploy-agent/.env
+```
+
+Edit paths:
+
+```env
+FRONTEND_DEPLOY_SOURCE_PATH=/opt/raspi-chat/source
+FRONTEND_DEPLOY_ADMIN_WEBROOT=/var/www/example_user/data/www/admin.example.ru
+FRONTEND_DEPLOY_WIDGET_WEBROOT=/var/www/example_user/data/www/widget.example.ru
+FASTPANEL_SAFE_MODE=true
+```
+
+## Run deploy manually
+
+From repository root on VPS:
+
+```bash
+npm install
+npm run deploy:frontend
+```
+
+## API reverse proxy
+
+For `api.example.ru`, configure FastPanel custom Nginx directives to proxy traffic through WireGuard to Raspberry Pi backend.
+
+Example target:
+
+```text
+http://10.8.0.2:3000
+```
+
+WebSocket path:
+
+```text
+/ws
+```
+
+Use FastPanel UI or a FastPanel-safe include file. Do not overwrite FastPanel generated configs directly.