ci: add publish workflow with frontend and backend deploy

publish.yml — triggered on push to main, two parallel jobs:

frontend:
- Builds Vite frontend (fnm + npm ci + npm run build)
- Rsyncs dist/ to gitea_ci@UI_HOST:UI_PATH/
- Rsyncs nginx config to UI_HOST, creates sites-enabled symlink,
  runs nginx -t && systemctl reload nginx

backend:
- Builds release binary (cargo build --release -p ericrfb-proxy)
- Stops blekin.service on WS_HOST
- Rsyncs binary to WS_HOST:/usr/local/bin/ericrfb-proxy via sudo rsync
- Rsyncs systemd unit to WS_HOST:/etc/systemd/system/blekin.service
- Enables and starts the service

asset/nginx/blekin.kosherinata.internal.conf:
- Serves static frontend from UI_PATH
- Reverse proxies /api/ to frootmig:3000 with WebSocket upgrade
- 24h read/send timeouts for long-lived KVM sessions

asset/systemd/blekin.service:
- Runs ericrfb-proxy with BLEKIN_HOST=10.3.0.130
- Restart on failure with 5s backoff

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

asset/nginx/blekin.kosherinata.internal.conf

@@ -0,0 +1,22 @@
+server {
+    listen 80;
+    server_name blekin.kosherinata.internal;
+
+    root /var/www/blekin.kosherinata.internal;
+    index index.html;
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    location /api/ {
+        proxy_pass http://frootmig.kosherinata.internal:3000;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_read_timeout 86400s;
+        proxy_send_timeout 86400s;
+    }
+}