CVE-2025-57808: ESP-IDF web_server basic auth bypass using empty or incomplete Authorization header

On the ESP-IDF platform, ESPHome’s web_server authentication check can pass incorrectly when the client-supplied base64-encoded Authorization value is empty or is a substring of the correct value (e.g., correct username with partial password). This allows access to web_server functionality (including OTA, if enabled) without knowing any information about the correct username or password.