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>

.vscode/extensions.json

@@ -0,0 +1,10 @@
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+    // for the documentation about the extensions.json format
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+        "platformio.platformio-ide"
+    ],
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+}