Move the nebula sky, planet surface and particle glow textures to VRAM
compression with mipmaps, so they stop being uploaded uncompressed.
The sky panorama is forced to high quality (BC7). It is a 5 MB image of
smooth nebula gradients seen through the arena walls, and BC1/BC3's 5:6:5
endpoint interpolation bands visibly across exactly that kind of content.
Extend gen_nebula_sky.py with two more dust-lane layers at different
scales and subtle hue variation within the bright core. Add
gen_planet_surface.py (no prior generator existed) producing latitude
bands, storm vortices, and a lit/unlit terminator baked from the
planet mesh's actual UV convention against arena_02's directional
light, verified in-engine via screenshots.
Every bright star in sky_nebula.png reused the exact same diffraction-
spike stamp, just relocated. Commit the generator (recovered from an
ephemeral scratchpad) to tools/textures/gen_nebula_sky.py, randomize
each hero star's rotation, arm count, spike length, and brightness,
and regenerate the texture.
Introduce arena_02 (Nebula) and arena_03 (Asteroid Field) alongside
arena_01, listed in a new ArenaRegistry (scripts/arena_registry.gd) as
the single source of truth for available arenas. Free Play lets the
player pick an arena from the main menu; Match/Spectate each pick one
at random per session; Training keeps its own fixed arena_01.
Nebula gets an RL-style visual treatment: a near-invisible glass
boundary material shared by all arenas, a baked equirect nebula sky
texture, a drifting-dust particle system, and a Blender-modeled
station/debris/planet decoration set. GameMode gains a
_get_arena_scene_path() hook so modes can instantiate their arena in
code instead of hardcoding it in the scene.