Fix V3 bootloop: DIO flash mode, auto-verify, boot monitoring

- V3 board profile defaults to DIO flash mode (QIO fails on some flash chips)
- flash.py: auto-verify on --erase/--full, post-flash boot monitoring with
  auto-DIO retry on bootloop detection
- flash.py: erase keeps device in download mode (--after no_reset) to prevent
  race condition on re-entry
- flash.py: remove --dio/--verify flags (now automatic), hidden --flash-mode
  for power users
- RNode_Firmware.ino: release BT memory (~70KB) on V3 boundary where BT is
  compile-time disabled
- RNode_Firmware.ino: add WDT resets throughout setup() to prevent timeout
  during long init sequences
- RNode_Firmware.ino: fix while-not-Serial blocking on V3 (no USB-CDC)
- RNode_Firmware.ino: init bt_devname from WiFi MAC when BT disabled
- RNode_Firmware.ino: bootloop detection via RTC_NOINIT_ATTR -- forces config
  portal after 5 rapid reboots

Utilities.h

@@ -1887,7 +1887,7 @@ void unlock_rom() {
 
 void init_channel_stats() {
 	#if MCU_VARIANT == MCU_ESP32
-		for (uint16_t ai = 0; ai < DCD_SAMPLES; ai++) { util_samples[ai] = false; }
+		memset(util_samples, 0, DCD_BITFIELD_SIZE);
 		for (uint16_t ai = 0; ai < AIRTIME_BINS; ai++) { airtime_bins[ai] = 0; }
 		for (uint16_t ai = 0; ai < AIRTIME_BINS; ai++) { longterm_bins[ai] = 0.0; }
 		local_channel_util = 0.0;