fix(V4B): debug打印t=0ms bug + freeze_ref残留清零 (V4.20)

日志复现: DBG行t恒为0(先归零后打印) — 改为先取时间再归零
         FRZ=0/129058 ref残留(正常跟踪未清) — 对称窗口分支补 freeze_ref=0
无功能影响, 仅打印正确性/美观

utilities/at32f421_freertos_demo/src/TaskLoop.c

@@ -777,6 +777,7 @@ void vd1_task(void)
             if (dev < freeze_band && dev > -freeze_band) {
                 /* 对称窗口内 → 正常基线跟踪 */
                 loop1_freeze_cnt = 0;
+                loop1_freeze_ref = 0;      // V4.20: 清残留参考, 打印 FRZ 干净
                 update_moving_average(&loop1_ORG_SUM, &loop1_ORG_CNT,
                                       &loop1_Origin, loop1_CAPVD, WINDOW_ORIGIN);
             } else if (dev < 0) {
@@ -1041,10 +1042,11 @@ void loop_task_function(void *pvParameters)
             static uint32_t _dbg_cnt = 0;
             _dbg_cnt++;
             if (_dbg_cnt >= 200) {      // 200 × 10ms = 2s
+                uint32_t _t_ms = _dbg_cnt * 10;   // V4.20: 先取时间再归零
                 _dbg_cnt = 0;
                 PRINT("DBG|t=%ums f=%dkHz Xn=%d LPCNT=%d Value=%d CAPVD=%d slow=%d "
                       "Origin=%d dlt=%d SENS=%d VD=%d FRZ=%d/%d LIM=%d LOOP=%d STBL=%d\n",
-                      _dbg_cnt * 10,
+                      _t_ms,
                       calc_freq_khz(loop1_CAPVD, loop1_LPCNT),
                       loop1_Xn, loop1_LPCNT, loop1_Value, loop1_CAPVD, loop1_CAPVD_slow,
                       loop1_Origin, loop1_dlt_ORG, loop1_SensLevel, loop1_VD_FLAG,