v0.4.0 - Battery Fix, Remote CLI & Flash Optimization

What's New in v0.4.0

Bug Fixes

• Battery ADC fixed - Resolved 0V battery reading caused by
  CubeCell framework 1.6.0 bug (ch3 SAR calibration not initialized).
  New workaround uses analogRead() + ch0 calibration + VBAT_ADC_CTL
  circuit control
• Airtime tracking - RX/TX airtime now properly calculated
  per-packet using LoRa formula
• Noise floor estimation - EMA-smoothed noise floor from
  RSSI-SNR, no longer stuck at 0dB
• Remote CLI commands - Fixed "Err:Unknown" for commands only
  available on local serial

New Features

• radiostats command - Noise floor, last RSSI/SNR, airtime
  TX/RX (serial + remote)
• packetstats command - Packet breakdown: flood/direct RX/TX
  (serial + remote)
• lifetime command - Now available via remote CLI (was
  serial-only)
• tempradio command - Temporary radio parameter changes without
  saving to EEPROM

Optimizations

• Flash savings: 2,904 bytes - String abbreviation in LOG/LOG_RAW
  macros (98.3% → 96.0%)
• Startup banner simplified (removed unicode box-drawing characters)

Documentation

• Complete command reference tables in README
• Corrected radio parameters (frequency, TX power, sync word)

Build Info

• Flash: 96.5% (126,492 / 131,072 bytes)
• RAM: 51.3% (8,408 / 16,384 bytes)
• Board: Heltec CubeCell HTCC-AB01
• Region: EU868