Nav map art, the sky between the systems, the map's spacing 5000 again

nav_prettymap.3db / zoomedmap_liberty.3db: the new sector map and system backdrop (REM-Client
tools/rem/import_navmap_art.py). remui/img: the galaxy view's picture and the interstellar sky's pictures
(sky_base.png, sky_sirius.png - REM-Client 5149b6fa, 0a38d050). rem.ini: interstellar_sky (which parts of
that sky draw). sectors.ini: spacing 5000, as the server's again (2 million km between neighbours).

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

DATA/UNIVERSE/sectors.ini

@@ -3,7 +3,7 @@
 ; universe.ini [system] navmap_shape = square | round overrides a sector's system_shape.
 
 [Map]
-spacing = 2500                  ; the world map's spacing for the map (a server with a world map sends its own placements)
+spacing = 5000                  ; the world map's spacing for the map (a server with a world map sends its own placements)
 
 [Galaxy]
 sun_from_center_ly = 26000      ; Sol to the galactic centre, in the Orion Arm