ESP-NOW: STA interface, notify browser on send failure

- Activate STA interface before ESP-NOW to fix ESP_ERR_ESPNOW_IF
- Notify browser on send failure: WebSocket sends error JSON; preset API returns 503
- Use exceptions for failure (not return value) to avoid false errors when send succeeds
- presets.js: handle server error messages in WebSocket onmessage

Made-with: Cursor

src/models/espnow.py

@@ -1,3 +1,5 @@
+import network
+
 import aioespnow
 
 
@@ -20,11 +22,17 @@ class ESPNow:
         if getattr(self, "_initialized", False):
             return
 
-        # Initialize ESPNow once (no disk persistence)
+        # ESP-NOW requires a WiFi interface to be active (STA or AP). Activate STA
+        # so ESP-NOW has an interface to use; we don't need to connect to an AP.
+        try:
+            sta = network.WLAN(network.STA_IF)
+            sta.active(True)
+        except Exception as e:
+            print("ESPNow: STA active failed:", e)
+
         self._esp = aioespnow.AIOESPNow()
         self._esp.active(True)
 
-   
         try:
             self._esp.add_peer(b"\xff\xff\xff\xff\xff\xff")
         except Exception:
@@ -56,6 +64,6 @@ class ESPNow:
         try:
             await self._esp.asend(b"\xff\xff\xff\xff\xff\xff", payload)
         except Exception as e:
-            # Log send failures but don't crash the app
             print("ESPNow.send error:", e)
+            raise