Clarify Service Contracts And Security Invariants

src/wifi_config.h

@@ -5,6 +5,8 @@
  * The public structures below are also the version-1 NVS wire format. Keep
  * every field fixed-width and introduce a new schema version for layout
  * changes; do not silently reinterpret an existing blob.
+ * Config copies contain plaintext PSKs: never use them for routine status/logs,
+ * and wipe transient copies with wifi_config_secure_wipe() when finished.
  */
 
 #pragma once
@@ -77,6 +79,7 @@ typedef struct {
     uint8_t ap_channel;
     uint8_t reserved[5];
 
+    /* As for station profiles, lengths are authoritative; no NUL is required. */
     uint8_t ap_ssid[WIFI_CONFIG_SSID_MAX_LEN];
     uint8_t ap_psk[WIFI_CONFIG_PSK_MAX_LEN];
     uint8_t reserved_tail[1];