feat(vd960DBN)+fix(DBNMQTTool): log_query 改 hex 原始字节上报 (2026-08-18)

背景: MQTT 快照流实测 MQTTSerialize_publish failed — JSON 化快照记录 ~810B/条 超 800B 发送缓冲
方案(用户拍板): 对齐 BLE 通道, 原始字节 hex 上报

固件 (V4.3):
- offlog.c/h: 新增 offlog_evt_to_hex() (32B→64 hex)
- snapshot.c/h: 新增 snap_rec_to_hex() (64B→128 hex); 删 SNAP_MAX_QUERY_JSON, 恢复 count=2
- tcp_json_srv.c / iot_mqtt_srv.c: log_query 改 {"seq":N,"hex":"..."}; SEND_BUF 保持 800
- 2 条快照 hex 响应 406B < 800B

文档: TCP JSON V1.03 / MQTT V1.07 §4.17 records 改 hex + 解析表引用 BLE §6.4/§7

工具: parse_offlog_hex/parse_snap_hex/offlog_payload_desc + hex 展示; 验证: gcc 9 断言 + 工具解析全过 + offscreen UI

vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/snapshot.c

@@ -480,3 +480,17 @@ int snap_rec_to_json(const SnapRec *r, char *buf, int buf_len)
     pos += snprintf(buf + pos, buf_len - pos, "]}");
     return pos;
 }
+
+/* SnapRec -> hex string (flash 原始字节, 小端原样; 上位机按 BLE 协议 §6.4 字段表解析)
+   Used by TCP JSON / MQTT log_query stream=snapshot (protocol V1.03/V1.07).
+   Returns snprintf written length; 64B -> 128 hex chars. */
+int snap_rec_to_hex(const SnapRec *r, char *buf, int buf_len)
+{
+    int i, pos = 0;
+    const uint8_t *p = (const uint8_t *)r;
+    for (i = 0; i < (int)sizeof(SnapRec); i++) {
+        if (pos >= buf_len - 3) break;
+        pos += snprintf(buf + pos, buf_len - pos, "%02x", p[i]);
+    }
+    return pos;
+}