Initial commit: ZNET Temperature Sensor ESP32 firmware

- PlatformIO project for Meshnology ESP32 LoRa V3
- DS18B20 dual sensor support for tank verification
- OLED display for local temperature visibility
- HTTP POST to ZNET Web API
- WiFiManager for easy WiFi configuration
- Offline buffering when network unavailable

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

platformio.ini

@@ -0,0 +1,51 @@
+; PlatformIO Project Configuration File
+; ZNET Temperature Sensor - ESP32 LoRa Gateway
+;
+; Board: Meshnology ESP32 LoRa V3 (Heltec-compatible)
+; Features: DS18B20 temp sensors, OLED display, LoRa RX, WiFi TX
+
+[env:heltec_wifi_lora_32_V3]
+platform = espressif32
+board = heltec_wifi_lora_32_V3
+framework = arduino
+
+; Serial monitor
+monitor_speed = 115200
+
+; Build flags
+build_flags =
+    -DCORE_DEBUG_LEVEL=3
+    -DARDUINO_USB_MODE=1
+    ; OLED display pins (Heltec V3)
+    -DOLED_SDA=17
+    -DOLED_SCL=18
+    -DOLED_RST=21
+    ; LoRa pins (SX1262)
+    -DLORA_SCK=9
+    -DLORA_MISO=11
+    -DLORA_MOSI=10
+    -DLORA_SS=8
+    -DLORA_RST=12
+    -DLORA_DIO1=14
+    -DLORA_BUSY=13
+    ; DS18B20 data pin
+    -DONEWIRE_PIN=7
+
+; Libraries
+lib_deps =
+    ; OneWire for DS18B20
+    paulstoffregen/OneWire@^2.3.8
+    ; Dallas Temperature library
+    milesburton/DallasTemperature@^3.11.0
+    ; OLED display (SSD1306)
+    thingpulse/ESP8266 and ESP32 OLED driver for SSD1306 displays@^4.6.1
+    ; HTTP client (built-in, but explicit)
+    ; JSON serialization
+    bblanchon/ArduinoJson@^7.2.1
+    ; LoRa radio (RadioLib for SX1262)
+    jgromes/RadioLib@^7.1.2
+    ; WiFi Manager for easy setup
+    tzapu/WiFiManager@^2.0.17
+
+; Upload settings
+upload_speed = 921600