The settings routes returned the WiFi passphrase, MQTT password and the
login password and PIN in plain text, and the debug log printed them and
the API key. Responses now carry hasPassphrase/hasPassword/hasPin flags,
logs mask the values, and an omitted secret keeps the stored one.
The UI loads secret fields empty and treats a blank field as "keep" while
the SSID or username is unchanged. Clearing a secret without changing the
SSID or username is listed in docs/KNOWN_ISSUES.md.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
