feat: auto-detect wss:// for rosbridge when page served over HTTPS (Issue #681)

- Default URL auto-selects wss://saul-t-mote.evthings.app/rosbridge when
  page is loaded via https://, falls back to ws://100.64.0.2:9090 for
  local/Tailscale access
- Clears hardcoded ws:// value from input; JS sets it from localStorage
  or the detected default on first load

Companion: nginx config on Orin adds /rosbridge WebSocket reverse proxy
  on port 8080  →  ws://127.0.0.1:9090

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

jetson/nginx/saul-tee.conf

@@ -0,0 +1,64 @@
+# saul-tee.conf — nginx site for saul-t-mote.evthings.app reverse proxy
+#
+# Replaces: python3 -m http.server 8080 --directory /home/seb
+# Router (ASUS Merlin / OpenResty) terminates TLS on :443 and proxies to Orin:8080
+#
+# Deploy:
+#   sudo cp saul-tee.conf /etc/nginx/sites-available/saul-tee
+#   sudo ln -sf /etc/nginx/sites-available/saul-tee /etc/nginx/sites-enabled/saul-tee
+#   sudo systemctl reload nginx
+#
+# ROUTER REQUIREMENT for WSS to work:
+#   The ASUS Merlin router's nginx/OpenResty must proxy /rosbridge with
+#   WebSocket headers.  Add to /jffs/configs/nginx.conf.add:
+#
+#     map $http_upgrade $connection_upgrade {
+#         default upgrade;
+#         ''      close;
+#     }
+#
+#   And in the server block that proxies to 192.168.86.158:8080, add:
+#
+#     location /rosbridge {
+#         proxy_pass         http://192.168.86.158:8080/rosbridge;
+#         proxy_http_version 1.1;
+#         proxy_set_header   Upgrade    $http_upgrade;
+#         proxy_set_header   Connection $connection_upgrade;
+#         proxy_read_timeout 86400;
+#     }
+
+# Infer WebSocket upgrade from Connection header.
+# Handles the case where an upstream proxy (e.g. ASUS Merlin OpenResty)
+# passes Connection: upgrade but strips the Upgrade: websocket header.
+map $http_connection $ws_upgrade {
+    "upgrade" "websocket";
+    default   "";
+}
+
+server {
+    listen 8080 default_server;
+    listen [::]:8080 default_server;
+
+    root /home/seb;
+    index index.html;
+    server_name _;
+
+    # Static files — replaces python3 -m http.server 8080 --directory /home/seb
+    location / {
+        try_files $uri $uri/ =404;
+        autoindex on;
+    }
+
+    # rosbridge WebSocket reverse proxy
+    # wss://saul-t-mote.evthings.app/rosbridge  -->  ws://127.0.0.1:9090
+    location /rosbridge {
+        proxy_pass         http://127.0.0.1:9090/;
+        proxy_http_version 1.1;
+        proxy_set_header   Upgrade    $ws_upgrade;
+        proxy_set_header   Connection "upgrade";
+        proxy_set_header   Host       $host;
+        proxy_set_header   X-Real-IP  $remote_addr;
+        proxy_read_timeout 86400;
+        proxy_send_timeout 86400;
+    }
+}