Initial commit: ESP32 NextPM sensor reader

Educational version with comprehensive comments for students.
- Reads PM1.0, PM2.5, and PM10 concentrations from NextPM sensor
- Uses UART serial communication with checksum validation
- Non-blocking timing with millis()
- Removed particle counts, kept only mass concentrations
- Extensively commented to help students understand serial protocols

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

platformio.ini

@@ -0,0 +1,15 @@
+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:esp32]
+platform = espressif32
+board = esp32dev
+monitor_speed = 115200
+framework = arduino