Remove gamma value lower limit to enable inverse gamma correction (#5187)

* Enable inverse gamma correction (gamma < 1.0)

Allow gamma values from 0.1 to 3.0 instead of restricting to > 1.0.
This enables inverse gamma curves for use cases requiring brightened
mid-tones and compressed highlights.

Changes:
- Update backend validation in set.cpp and cfg.cpp to accept 0.1-3.0
- Update HTML form min value from 1 to 0.1

Co-authored-by: Flo <flo@Mac.lan>
Co-authored-by: Damian Schneider <daedae@gmx.ch>

wled00/set.cpp

@@ -378,7 +378,7 @@ void handleSettingsSet(AsyncWebServerRequest *request, byte subPage)
     gammaCorrectBri = request->hasArg(F("GB"));
     gammaCorrectCol = request->hasArg(F("GC"));
     gammaCorrectVal = request->arg(F("GV")).toFloat();
-    if (gammaCorrectVal <= 1.0f || gammaCorrectVal > 3) {
+    if (gammaCorrectVal < 0.1f || gammaCorrectVal > 3) {
       gammaCorrectVal = 1.0f; // no gamma correction
       gammaCorrectBri = false;
       gammaCorrectCol = false;