Use a more realistic texture of the Sun

Current texture of the Sun looks cartoonish and doesn't reflect the real
look of the Sun. It not only has wrong colors, but also wrong granule
sizes and sunspot sizes, locations, and contrast.

The new texture is made from the SDO HMI observations, which
automatically fixes these issues. The texture is a result of stitching
the maps obtained from multiple HMI images, with the equatorial region
containing the sunspots taken from observations from 2025-08-07 to
2025-08-31, while the rest is filled with spotless data of 2019-12-15.
All the source images were considered valid only in the central 60% of
the solar disk, because outside that region the faculae become more
prominent, which is undesired for such a generic texture expected to be
viewed from different angles.

Author: 10110111

data/ssystem_major.ini

@@ -1767,7 +1767,7 @@ radius=696000.
 rot_equator_ascending_node=196.13
 rot_obliquity=7.25
 ;rot_periode=654.61
-tex_map=sun.png
+tex_map=sun.webp
 type=star
 rot_pole_ra=286.13
 rot_pole_de=63.87

textures/CMakeLists.txt

@@ -3,6 +3,7 @@
 INSTALL(DIRECTORY ./ DESTINATION ${SDATALOC}/textures
         FILES_MATCHING PATTERN "*.png"
         PATTERN "*.jpg"
+        PATTERN "*.webp"
         PATTERN "CMakeFiles" EXCLUDE )