torrents: document NPM web UI instance labels (OPEN/VPN badges)

torrents/NPM-WEBUI-LABELS.md

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+# qBittorrent Web UI Instance Labels
+
+The `open` and `vpn` instances are proxied via nginx-proxy-manager and have colored
+badges injected into the Web UI to distinguish them at a glance.
+
+## How it works
+
+nginx's `sub_filter` module replaces `</head>` in the HTML response with a `<style>`
+block that adds a fixed-position badge in the top-right corner of the page.
+
+**open** (qbto.kolpacksoftware.com) — blue badge
+**vpn** (qbtv.kolpacksoftware.com) — green badge
+
+## NPM Advanced tab config
+
+For each proxy host, the following is set in the **Advanced** tab:
+
+**open:**
+```nginx
+sub_filter '</head>' '<style>body::after{content:"OPEN";position:fixed;top:5px;right:5px;background:#1565c0;color:#fff;padding:3px 10px;border-radius:3px;font-size:13px;font-weight:bold;z-index:99999;font-family:monospace;pointer-events:none;}</style></head>';
+sub_filter_once on;
+proxy_set_header Accept-Encoding "";
+```
+
+**vpn:**
+```nginx
+sub_filter '</head>' '<style>body::after{content:"VPN";position:fixed;top:5px;right:5px;background:#2e7d32;color:#fff;padding:3px 10px;border-radius:3px;font-size:13px;font-weight:bold;z-index:99999;font-family:monospace;pointer-events:none;}</style></head>';
+sub_filter_once on;
+proxy_set_header Accept-Encoding "";
+```
+
+## Important: manual fix required after saving in NPM UI
+
+NPM regenerates the nginx conf file whenever you save a proxy host in the UI,
+which overwrites a necessary fix. After saving either proxy host, re-run:
+
+```bash
+# For open (proxy host 4):
+sudo sed -i 's|    include conf.d/include/proxy.conf;|    proxy_set_header Accept-Encoding "";\n    include conf.d/include/proxy.conf;|' /srv/nginx-proxy/data/nginx/proxy_host/4.conf
+
+# For vpn (proxy host 28):
+sudo sed -i 's|    include conf.d/include/proxy.conf;|    proxy_set_header Accept-Encoding "";\n    include conf.d/include/proxy.conf;|' /srv/nginx-proxy/data/nginx/proxy_host/28.conf
+
+docker exec nginx-proxy nginx -s reload
+```
+
+### Why is this needed?
+
+`proxy_set_header Accept-Encoding ""` must be inside the `location /` block for
+nginx to actually strip the header before forwarding to qBittorrent. When set at
+the server block level (via NPM's Advanced tab), it is silently ignored because
+the location block defines its own `proxy_set_header` directives via `proxy.conf`.
+
+Without this fix, qBittorrent returns gzip-compressed responses and `sub_filter`
+cannot process them, so the badge never appears.