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>

EXE/rem.ini

@@ -25,6 +25,7 @@ asteroid_quality = 3               ; view distance: 0 Low, 1 Medium, 2 High, 3 U
 
 ; ---- Physics ----
 draw_time_extrapolation = true     ; multiplayer: moving objects drawn as of the frame's time (false: as of the last physics step, retail)
+interstellar_sky = 7               ; multiplayer, between the systems: 1 the base star sphere, 2 the nebulae, 4 the suns (add them up; 0: none) - diagnostics
 
 ; ---- Cursor and mouse ----
 cursor_color = 0                   ; cursor colour: 0 game default, 1 red, 2 green, 3 blue, 4 yellow, 5 pink