Fix compass heading direction, add magnetic declination and heading offset

- Fix atan2 sign bug: atan2(-yHeading, xHeading) per Freescale AN4248 eq.22.
  The previous atan2(yHeading, xHeading) produced counter-clockwise angles,
  causing East/West to be swapped relative to compass convention.

- Add imuSetMagneticDeclination() (T:146, field "decl") to correct the
  offset between magnetic north and true north (iPhone shows true north).
  Value is persisted in imuConfig.json across reboots.

- Add imuSetHeadingOffset() (T:147, field "off") to compensate for sensor
  mounting orientation on the rover. Also persisted.

- Persist decl and hOff in imuConfig.json (version 2, backwards compatible).

- Fix calibration feedback for web interface: T:126 now includes calDone=1
  (success) or calDone=0 (fail) once after calibration completes, plus
  decl and hOff fields. Calibration start message explains polling procedure.

- Remove duplicate #include <nvs_flash.h> and unused Adafruit ICM20948
  includes that caused build failures when libraries were not installed.

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

WAVE_ROVER.ino

@@ -1,4 +1,4 @@
-#include <ArduinoJson.h>
+#include <ArduinoJson.h>
 StaticJsonDocument<256> jsonCmdReceive;
 StaticJsonDocument<256> jsonInfoSend;
 StaticJsonDocument<512> jsonInfoHttp;
@@ -12,16 +12,12 @@ StaticJsonDocument<512> jsonInfoHttp;
 #include <WiFi.h>
 #include <WebServer.h>
 #include <esp_now.h>
-#include <nvs_flash.h>
 #include <Adafruit_SSD1306.h>
 #include <INA219_WE.h>
 #include <ESP32Encoder.h>
 #include <PID_v2.h>
 #include <SimpleKalmanFilter.h>
 #include <math.h>
-#include <Adafruit_ICM20X.h>
-#include <Adafruit_ICM20948.h>
-#include <Adafruit_Sensor.h>
 
 
 // functions for barrery info.
@@ -119,7 +115,7 @@ void setup() {
     screenLine_0 = "UGV";
   } 
   
-  screenLine_1 = "version: 1.00";
+  screenLine_1 = "version: 1.00";
   screenLine_2 = "starting...";
   screenLine_3 = "";
   oled_update();
@@ -136,9 +132,9 @@ void setup() {
   screenLine_2 = screenLine_3;
   screenLine_3 = "Initialize LittleFS";
   oled_update();
-  if(InfoPrint == 1){Serial.println("Initialize LittleFS for Flash files ctrl.");}
-  initFS();
-  imuLoadMagnCalibration();
+  if(InfoPrint == 1){Serial.println("Initialize LittleFS for Flash files ctrl.");}
+  initFS();
+  imuLoadMagnCalibration();
 
   // init the funcs in switch_module.h
   screenLine_2 = screenLine_3;
@@ -265,4 +261,4 @@ void loop() {
   heartBeatCtrl();
 
   size_t freeHeap = esp_get_free_heap_size();
-}
+}