feat: allow multiple concurrent WS clients (web UI + app)

The previous middleware returned 503 to any client past the first,
which meant opening the on-device web UI prevented a phone/desktop
app from connecting to the same scale. Drop the cap and let the
library handle multi-client.

  * include/webserver.h: remove the count-checking middleware so any
    handshake within the library's DEFAULT_MAX_WS_CLIENTS limit
    succeeds.
  * src/hds.ino: call websocket.cleanupClients() with no argument so
    we inherit the library default (DEFAULT_MAX_WS_CLIENTS, which is
    8 on ESP32). Plenty of RAM headroom — ~12-14 KB per client on
    top of ~240 KB free heap.
  * src/hds.ino WS_EVT_DISCONNECT: only reset the shared session
    state (weightWebsocketNotifyInterval, b_websocketEventsEnabled,
    t_lastWebsocketStatusUpdate) when the LAST client leaves
    (server->count() == 0). Without this guard, one client
    disconnecting would wipe rate/events state for any other client
    still connected.

Verified with /tmp/ws_multi.py (5/5):
  * Two simultaneous handshakes both succeed (was: 2nd got 503).
  * Both clients receive the weight stream at the negotiated rate
    (2Hz default, 10Hz after `rate 10`).
  * Both clients see the periodic status broadcast after `events on`.
  * Disconnecting client A leaves client B's stream + state intact.

Single-client feature regression still 60/60 PASS.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: skialpine

include/webserver.h

@@ -39,16 +39,10 @@ void startWebServer() {
         });
     server.addHandler(wifiHandler);
 
-    server.addHandler(&websocket).addMiddleware([](AsyncWebServerRequest *request, ArMiddlewareNext next) {
-      // ws.count() is the current count of WS clients: this one is trying to upgrade its HTTP connection
-      if (websocket.count() > 0) {
-        // if we have 1 clients or more, prevent the next one to connect
-        request->send(503, "text/plain", "Server is busy");
-      } else {
-        // process next middleware and at the end the handler
-        next();
-      }
-    });
+    // Allow multiple concurrent WebSocket clients (e.g. the on-device web UI
+    // and a separate desktop/phone app at the same time). Per-loop the count
+    // is bounded by cleanupClients() in src/hds.ino.
+    server.addHandler(&websocket);
 
     if (!LittleFS.begin()) {
       Serial.println("LittleFS mount failed");

src/hds.ino

@@ -958,9 +958,15 @@ void _wifi_init(void *args) {
       client->setCloseClientOnQueueFull(false);
     } else if (type == WS_EVT_DISCONNECT) {
       Serial.printf("Client %u disconnected\n", client->id());
-      weightWebsocketNotifyInterval = WEBSOCKET_DEFAULT_NOTIFY_INTERVAL_MS;
-      b_websocketEventsEnabled = false;
-      t_lastWebsocketStatusUpdate = 0;
+      // Only reset shared session state when the LAST client leaves —
+      // otherwise one client disconnecting would wipe rate/events state
+      // for any other still-connected clients. server->count() at this
+      // point excludes the disconnecting client.
+      if (server->count() == 0) {
+        weightWebsocketNotifyInterval = WEBSOCKET_DEFAULT_NOTIFY_INTERVAL_MS;
+        b_websocketEventsEnabled = false;
+        t_lastWebsocketStatusUpdate = 0;
+      }
     } else if (type == WS_EVT_ERROR) {
       Serial.printf("WebSocket error on client %u\n", client->id());
     } else if (type == WS_EVT_PONG) {
@@ -1987,7 +1993,9 @@ void loop() {
           }
         }
         if (b_wifiEnabled) {
-          websocket.cleanupClients(1);
+          // Cap concurrent WS clients at the library default
+          // (DEFAULT_MAX_WS_CLIENTS = 8 on ESP32, 4 on ESP8266).
+          websocket.cleanupClients();
           ElegantOTA.loop();
           static unsigned long lastUpdate = 0;
           unsigned long current = millis();