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

Config.h

@@ -186,7 +186,8 @@
 		#define AIRTIME_LONGTERM_MS (AIRTIME_LONGTERM*1000)
 		#define AIRTIME_BINLEN_MS (STATUS_INTERVAL_MS*DCD_SAMPLES)
 		#define AIRTIME_BINS ((AIRTIME_LONGTERM*1000)/AIRTIME_BINLEN_MS)
-		bool util_samples[DCD_SAMPLES];
+		#define DCD_BITFIELD_SIZE ((DCD_SAMPLES + 7) / 8)
+		uint8_t util_samples[DCD_BITFIELD_SIZE];
 		uint16_t airtime_bins[AIRTIME_BINS];
 		float longterm_bins[AIRTIME_BINS];
 		int dcd_sample = 0;