Upgrade ESPAsyncWebServer from v3.11.0 to v3.11.1

Patches CWE-190 DoS vulnerability via specially crafted multipart
boundary parameter (ESP32Async/ESPAsyncWebServer#445). Directly
applicable since the firmware accepts multipart POSTs for OTA and
config restore endpoints.

Closes #481

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

Author: BrentIO

libraries.yaml

@@ -31,7 +31,7 @@ libraries:
     version: "2.0.2"
     url: "https://github.com/arduino-libraries/Ethernet"
   - name: "ESPAsyncWebServer"
-    version: "v3.11.0"
+    version: "v3.11.1"
     url: "https://github.com/ESP32Async/ESPAsyncWebServer"
   - name: "BrentIO_esp32OTA"
     version: "2026.05.06"