Remove gamma value lower limit to enable inverse gamma correction

[flo269]

Summary

Remove the artificial restriction that prevents gamma values below 1.0, enabling inverse gamma correction.

Motivation

LEDs can appear too dark at low brightness levels. Inverse gamma correction (gamma < 1.0) is needed to brighten the lower end of the brightness curve and make dimmed LEDs more visible.

Currently, gamma values are restricted to > 1.0, which only allows standard gamma correction. This PR removes that limitation.

Changes

• Update validation in set.cpp and cfg.cpp to allow gamma range 0.1-3.0 (was 1.0-3.0)
• Update HTML form validation in settings_leds.htm to match (min="0.1")

Technical Details

The NeoGammaWLEDMethod::calcGammaTable() function already supports any gamma value mathematically. This PR simply removes an artificial restriction that prevented values < 1.0.

Testing

Tested on v0.15.3 and latest main - inverse gamma values (< 1.0) now work correctly and improve visibility at low brightness levels.

Summary by CodeRabbit

• Bug Fixes
  • Expanded valid gamma correction range to accept values from 0.1 to 3.0; values between 0.1 and 1.0 are now preserved rather than being reset.
  • Updated the gamma value input to allow a minimum of 0.1 and adjusted its placeholder to reflect the finer calibration range.

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[coderabbitai]

Walkthrough

Lowered the minimum acceptable gamma correction from 1.0 to 0.1 in validation and UI, so gammaCorrectVal is accepted in [0.1, 3]; out-of-range values still reset gamma flags and trigger gamma-table recalculation/fallback.

Changes

Cohort / File(s)	Summary
Gamma validation & runtime handling wled00/cfg.cpp, wled00/set.cpp	Changed lower-bound check for gammaCorrectVal so values ≥ 0.1 and ≤ 3 are accepted (<= 1.0f → < 0.1f logic adjusted); out-of-range values continue to reset gammaCorrectBri/gammaCorrectCol and recalc fallback gamma tables.
Web UI input constraint wled00/data/settings_leds.htm	Updated gamma input min attribute from 1 to 0.1 and adjusted placeholder from 2.8 to 2.2 to match accepted backend range.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• add inverse gamma 32 function and fix colors in pride #4722: Modifies gamma validation/behavior in cfg.cpp and related gamma logic.
• Add pre-applied gamma to c3g & (some) fastled palettes to match original look #4711: Adjusts default gammaCorrectVal and palette pre-gamma handling; touches gamma defaults and UI.
• Fix gamma correction for color not enabled on fresh install #5225: Changes gamma-correction logic and explicit toggling of gamma flags on load; overlaps with gammaCorrectVal handling.

Suggested reviewers

• blazoncek

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main objective of the PR—removing the gamma value lower limit to enable inverse gamma correction values below 1.0. It aligns with the actual changes across all three modified files.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[DedeHai]

Did you check both gamma functions create correct tables for the new range?

[DedeHai]

I checked the functions, they do work still.
you also need to update the other lines in the config so it works after a reboot.

[flo269]

I think I have it figured out - updated lines 511 and 513 to check != 1.0f instead of > 1.0f so gamma correction is enabled for any non-linear value (both below and above 1.0). This should fix the persistence issue after reboot.

[tablatronix]

Any more testing needed for this? Seems like a low impact change