F-40: WiFi credentials saved before they work; set_config error reboots the device #43

Severity: LOW · Effort: Small · Batch: 3 · Status: Code done in #21 (b35b84c), awaiting bench verification

Found in the second full review of the firmware. Recorded with the rest of the pass (F-19…F-44) in docs/REVIEW_REMEDIATION_PLAN_2.md, which is where its status is kept.

WiFiManager::connect saves credentials before it knows they work, overwriting a good password
with a typo; and ESP_ERROR_CHECK(esp_wifi_set_config) turns a recoverable error into a reboot.

Acceptance Criteria

• Credentials entered on the screen are saved on IP_EVENT_STA_GOT_IP, read back from the
  driver; the stored-credential path saves nothing.
• A failed esp_wifi_set_config reports FAILED and returns the error.
• Bench: enter a wrong password over a working network, reboot; the device rejoins the
  working network.