Add comprehensive guides for new module, sensor, and hardware variant development

.github/prompts/new-sensor.prompt.md

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+# New Telemetry Sensor
+
+Guide for adding a new I2C telemetry sensor driver to Meshtastic firmware.
+
+## Overview
+
+Telemetry sensors live in `src/modules/Telemetry/Sensor/`. There are 50+ existing drivers organized by measurement type. Each sensor integrates with one of the telemetry modules:
+
+- **EnvironmentTelemetryModule** — Temperature, humidity, pressure, gas, light
+- **AirQualityTelemetryModule** — Particulate matter, VOCs
+- **PowerTelemetryModule** — Voltage, current, power monitoring
+- **HealthTelemetryModule** — Heart rate, SpO2, body temperature
+
+## Sensor Driver Pattern
+
+Each sensor has a `.h` and `.cpp` file pair following this pattern:
+
+```cpp
+// src/modules/Telemetry/Sensor/MySensor.h
+#pragma once
+#include "TelemetrySensor.h"
+#include <MySensorLibrary.h>  // Arduino/PlatformIO library
+
+class MySensor : virtual public TelemetrySensor
+{
+  private:
+    MySensorLibrary sensor;
+
+  public:
+    MySensor() : TelemetrySensor(meshtastic_TelemetrySensorType_MY_SENSOR, "MySensor") {}
+
+    // Initialize sensor hardware. Return true on success.
+    virtual void setup() override;
+
+    // Read sensor data into the telemetry protobuf. Return true on success.
+    virtual bool getMetrics(meshtastic_Telemetry *measurement) override;
+};
+```
+
+```cpp
+// src/modules/Telemetry/Sensor/MySensor.cpp
+#include "MySensor.h"
+#include "TelemetrySensor.h"
+
+void MySensor::setup()
+{
+    sensor.begin();
+    // Configure sensor parameters...
+}
+
+bool MySensor::getMetrics(meshtastic_Telemetry *measurement)
+{
+    // Read from hardware
+    float value = sensor.readValue();
+
+    // Populate the appropriate protobuf variant
+    measurement->variant.environment_metrics.temperature = value;
+    // ... other fields ...
+
+    return true;
+}
+```
+
+## I2C Address Registration
+
+Register the sensor's I2C address(es) in `src/detect/ScanI2C` so it's auto-detected at boot:
+
+1. Add a `DeviceType` enum entry in `src/detect/ScanI2C.h`
+2. Add the I2C address mapping in `src/detect/ScanI2CTwoWire.cpp`
+
+The scan runs at boot and populates a device map that telemetry modules use to decide which sensors to initialize.
+
+## Protobuf Fields
+
+If the sensor provides data not covered by existing telemetry fields:
+
+1. Add fields to the appropriate message in `protobufs/meshtastic/telemetry.proto`:
+   - `EnvironmentMetrics` — Environmental measurements
+   - `AirQualityMetrics` — Air quality data
+   - `PowerMetrics` — Power/energy data
+   - `HealthMetrics` — Health/biometric data
+2. Add a `.options` constraint if needed (field sizes for nanopb)
+3. Regenerate: `bin/regen-protos.sh`
+
+## Sensor Type Enum
+
+Add the sensor to `meshtastic_TelemetrySensorType` enum in `protobufs/meshtastic/telemetry.proto`:
+
+```protobuf
+enum TelemetrySensorType {
+    // ... existing entries ...
+    MY_SENSOR = XX;
+}
+```
+
+## Integration with Telemetry Module
+
+Wire the sensor into the appropriate telemetry module. For environment sensors, this is typically in `src/modules/Telemetry/EnvironmentTelemetry.cpp`:
+
+1. Include the sensor header
+2. Add initialization in `setupSensor()` guarded by detection results
+3. Call `getMetrics()` in the measurement collection path
+
+Example pattern from existing sensors:
+
+```cpp
+#include "Sensor/MySensor.h"
+
+MySensor mySensor;
+
+// In setup:
+if (nodeTelemetrySensorsMap[meshtastic_TelemetrySensorType_MY_SENSOR].first > 0) {
+    mySensor.setup();
+}
+
+// In measurement collection:
+if (nodeTelemetrySensorsMap[meshtastic_TelemetrySensorType_MY_SENSOR].first > 0) {
+    mySensor.getMetrics(&measurement);
+}
+```
+
+## Library Dependencies
+
+If the sensor needs an external library, add it to the `lib_deps` in the relevant base platformio.ini configs:
+
+```ini
+lib_deps =
+    ${env.lib_deps}
+    mysensorlibrary@^1.0.0
+```
+
+Or use a conditional dependency if it's platform-specific.
+
+## Unit Conversions
+
+If the sensor reports values in non-standard units, use `src/modules/Telemetry/UnitConversions.h` for conversion helpers (e.g., Celsius ↔ Fahrenheit, hPa ↔ inHg).
+
+## Checklist
+
+- [ ] Create `src/modules/Telemetry/Sensor/MySensor.h` and `.cpp`
+- [ ] Inherit from `TelemetrySensor` base class
+- [ ] Implement `setup()` and `getMetrics()` methods
+- [ ] Add `meshtastic_TelemetrySensorType` enum entry in `telemetry.proto`
+- [ ] Add I2C address to `src/detect/ScanI2C` for auto-detection
+- [ ] Add protobuf fields in `telemetry.proto` if new data types needed
+- [ ] Regenerate protos: `bin/regen-protos.sh`
+- [ ] Wire into the appropriate telemetry module (Environment/AirQuality/Power/Health)
+- [ ] Add library dependency if external library required
+- [ ] Test on hardware or native build