Sensors page: show placeholders for all connected sensors; support all LPP types

- SensorManager::getAvailableLPPTypes() reports which LPP types will be
  present based on initialized sensor flags (temp, humidity, pressure, etc.)
- Sensors page renders one row per available type; shows "--" for any sensor
  that hasn't produced a reading yet instead of hiding the row entirely
- LPPReader: add readLuminosity, readPercentage, readConcentration, readDistance
- All known LPP types now have proper names and units in the sensor display

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/helpers/SensorManager.h

@@ -23,6 +23,7 @@ public:
   virtual const char* getSettingValue(int i) const { return NULL; }
   virtual bool setSettingValue(const char* name, const char* value) { return false; }
   virtual LocationProvider* getLocationProvider() { return NULL; }
+  virtual int getAvailableLPPTypes(uint8_t* types, int max_count) const { return 0; }
 
   // Helper functions to manage setting by keys (useful in many places ...)
   const char* getSettingByKey(const char* key) {

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -540,6 +540,46 @@ bool EnvironmentSensorManager::querySensors(uint8_t requester_permissions, Cayen
 }
 
 
+int EnvironmentSensorManager::getAvailableLPPTypes(uint8_t* types, int max_count) const {
+  int n = 0;
+  auto add = [&](uint8_t t) { if (n < max_count) types[n++] = t; };
+
+  add(LPP_VOLTAGE);  // battery voltage — always present
+
+#if ENV_INCLUDE_GPS
+  add(LPP_GPS);
+#endif
+
+  bool has_temp = AHTX0_initialized || BME680_initialized || BME280_initialized ||
+                  BMP280_initialized || SHTC3_initialized || SHT4X_initialized ||
+                  LPS22HB_initialized || MLX90614_initialized || BMP085_initialized ||
+                  RAK12035_initialized;
+  if (has_temp) add(LPP_TEMPERATURE);
+
+  bool has_hum = AHTX0_initialized || BME680_initialized || BME280_initialized ||
+                 SHTC3_initialized || SHT4X_initialized || RAK12035_initialized;
+  if (has_hum) add(LPP_RELATIVE_HUMIDITY);
+
+  bool has_press = BME680_initialized || LPS22HB_initialized;
+  if (has_press) add(LPP_BAROMETRIC_PRESSURE);
+
+  bool has_alt = BME680_initialized || BME280_initialized || BMP280_initialized || BMP085_initialized;
+  if (has_alt) add(LPP_ALTITUDE);
+
+  bool has_power = INA3221_initialized || INA219_initialized || INA260_initialized || INA226_initialized;
+  if (has_power) { add(LPP_CURRENT); add(LPP_POWER); }
+
+#if ENV_INCLUDE_VL53L0X
+  if (VL53L0X_initialized) add(LPP_DISTANCE);
+#endif
+
+#if ENV_INCLUDE_RAK12035
+  if (RAK12035_initialized) add(LPP_PERCENTAGE);
+#endif
+
+  return n;
+}
+
 int EnvironmentSensorManager::getNumSettings() const {
   int settings = 0;
   #if ENV_INCLUDE_GPS

src/helpers/sensors/EnvironmentSensorManager.h

@@ -49,6 +49,7 @@ public:
   #endif
   bool begin() override;
   bool querySensors(uint8_t requester_permissions, CayenneLPP& telemetry) override;
+  int getAvailableLPPTypes(uint8_t* types, int max_count) const override;
   #if ENV_INCLUDE_GPS
   void loop() override;
   #endif

src/helpers/sensors/LPPDataHelpers.h

@@ -136,6 +136,22 @@ public:
     m = getFloat(&_buf[_pos], 2, 1, true); _pos += 2;
     return _pos <= _len;
   }
+  bool readLuminosity(float& lux) {
+    lux = getFloat(&_buf[_pos], 2, 1, false); _pos += 2;
+    return _pos <= _len;
+  }
+  bool readPercentage(float& pct) {
+    pct = getFloat(&_buf[_pos], 1, 1, false); _pos += 1;
+    return _pos <= _len;
+  }
+  bool readConcentration(float& ppm) {
+    ppm = getFloat(&_buf[_pos], 2, 1, false); _pos += 2;
+    return _pos <= _len;
+  }
+  bool readDistance(float& m) {
+    m = getFloat(&_buf[_pos], 4, 1000, false); _pos += 4;
+    return _pos <= _len;
+  }
 
   void skipData(uint8_t type) {
     switch (type) {