Add non-linear position estimation for RTS roller shades

Motor speed varies with drum radius as shade material winds/unwinds,
causing linear time-interpolation to misestimate position. Adds two
optional calibration fields (upMidTime, downMidTime) that let users
provide the elapsed time at 50% travel. A logarithmic model (alpha
ratio solved via Newton's method) then replaces the linear formula.
Falls back to existing linear behaviour when mid-time fields are zero.

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

.gitignore

@@ -8,3 +8,16 @@ SomfyController.ino.XIAO_ESP32S3.bin
 SomfyController.ino.esp32c3.bin
 SomfyController.ino.esp32s2.bin
 .vscode/settings.json
+.pio/
+.generated_files/
+build/
+dist/
+nbproject/
+Makefile*
+Package-*
+private/
+_build/
+!cmake/**/user.cmake
+cmake/**/.generated/*
+cmake/**/CMake*
+out/

Somfy.h

@@ -314,6 +314,11 @@ class SomfyShade : public SomfyRemote {
     uint32_t upTime = 10000;
     uint32_t downTime = 10000;
     uint32_t tiltTime = 7000;
+    uint32_t upMidTime = 0;   // Time (ms) from 100% to 50% when opening; 0 = linear
+    uint32_t downMidTime = 0; // Time (ms) from 0% to 50% when closing;  0 = linear
+    float alphaUp = 0.0f;     // Derived from upMidTime/upTime; 0 = use linear
+    float alphaDown = 0.0f;   // Derived from downMidTime/downTime; 0 = use linear
+    void computeAlphas();
     uint16_t stepSize = 100;
     bool save();
     bool isIdle();