TankSync v3.6.8

Adds firmware for the new 3.3 V transmitter board, and fixes power
reporting for any transmitter built without an INA219.

New: 3.3 V transmitter board support

There are now two transmitter PCBs in service, and they drive the GPIO10
sensor-rail gate with opposite polarity:

• 5 V board — GPIO10 feeds an AO3400 N-FET inverter stage. Active-HIGH.
• 3.3 V board — GPIO10 drives an AO3401 P-FET directly, no inverter.
  Active-LOW.

One binary cannot serve both. Flashing the 5 V image onto a 3.3 V board
inverts the gate and leaves the sensor rail powered continuously, which
defeats the sleep budget entirely.

Each release now ships four transmitter images instead of two:

Asset	Board	Radio
tanksync-transmitter-lora-esp32c3-*	5 V	LoRa
tanksync-transmitter-lite-espnow-esp32c3-*	5 V	ESP-NOW Lite
tanksync-transmitter-lora-esp32c3-3v3-*	3.3 V	LoRa
tanksync-transmitter-lite-espnow-esp32c3-3v3-*	3.3 V	ESP-NOW Lite

Pick the image that matches your board. The board axis is independent
of the radio, so both radios get both flavours. Existing 5 V boards are
unaffected — those binaries are built exactly as before.

Fixed: transmitters without an INA219 reported "Mains powered"

A transmitter with no power-monitoring chip fitted reported
POWER_MODE_NONE, which the app rendered as "Mains powered" — on boards
that have no mains input at all. That also suppressed solar charge
reporting, because the charging flag is only published when a battery is
detected.

• On the 3.3 V board, a low bus-voltage reading is now treated as a bad
  sample rather than as evidence of mains. This board is fed from the cell
  through the TPS63802 and nothing else, so "running on external 5 V" is
  not a reachable state. The last good reading is held across deep sleep
  instead of reporting 0 %.
• The INA219 probe retries instead of latching POWER_MODE_NONE on a single
  missed ACK at boot.
• Battery protection no longer switches off when a reading fails. The
  3.1 V cutoff and low-battery backoff previously shared a flag with
  battery presence, so a failed read silently disabled both.

Companion app fix: "Mains powered" is now shown only when the transmitter
actually reports mains, not when power monitoring is simply absent.

Upgrading

Existing 5 V boards can update over the air as usual. If you have a 3.3 V
board, flash the matching -3v3- image — a full-flash -full.bin is
attached for first-time programming at offset 0x0.

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Downloads (every variant for this firmware version)

Transmitter — ESP32-C3 SuperMini

• …-transmitter-lora-esp32c3-<tag>.bin — LoRa SKU (RYLR998 module)
• …-transmitter-lite-espnow-esp32c3-<tag>.bin — Lite SKU (ESP-NOW, built-in radio, no module)

Receiver / Hub

• …-receiver-esp32-<tag>.bin — ESP32 DevKit
• …-receiver-esp32s3-<tag>.bin — ESP32-S3 SuperMini

Each variant ships two images:

• plain .bin — OTA app image, flash at 0x10000, or use the one-click browser flasher / in-app OTA.
• …-full.bin — full-flash image for a fresh/blank board, flash at 0x0 with esptool: esptool.py write_flash 0x0 <file>-full.bin.