Fix colormap generation and selection stability

[GoulagmanYt]

-Fixed lazy colormap generation (no double-lock) and ensured all packaged gradients (agama/cmasher/cmocean/colorcet/hpluv/matplotlib) generate on demand with current LED gamma.

-Normalized handling of colormap names while keeping raw LCD values (e.g., “Rainbow ”) so both web UI and LCD can switch colormaps without crashes or stale lookups.

-On change (web or LCD), colormaps are now generated immediately; Rainbow/Velocity modes force-safe fallback if a LUT is missing.