fix: de-duplicate hero star diffraction-spike stamps in nebula sky

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.

TODO.md

@@ -29,10 +29,10 @@ The training pipeline is built — see `TRAINING.md` (self-play PPO via the vend
 
 A subagent ran the game and critiqued arena_02 head-on against Rocket League 2 in Unreal Engine 5: verdict was "a flat-shaded, unlit-looking blockout dressed up with two nice noise textures" — not fundamentally unfixable in Godot (SDFGI/Nanite-tier GI and hero-sculpted geometry aside), but several concrete gaps. Work through these one at a time, in this order (cheapest/highest-impact first). Each item has a ready-to-use prompt — paste it into a fresh session to tackle just that piece. The texture-generation Python scripts used for `sky_nebula.png`/`planet_surface.png` currently only exist in an ephemeral scratchpad, not the repo — the first item that touches them should commit a copy into the repo (e.g. `tools/textures/`) so they're reproducible.
 
-- [ ] **Post-processing pipeline** (no models needed — cheapest, highest-impact item on the list). Nothing currently sits on top of the raw render: no bloom/glow, no AA, no color grading, no vignette beyond the floor's baked fade.
+- [x] **Post-processing pipeline** (no models needed — cheapest, highest-impact item on the list). Nothing currently sits on top of the raw render: no bloom/glow, no AA, no color grading, no vignette beyond the floor's baked fade.
   Prompt: "In Cosmic Clash (Godot 4.7), the arena Environment resources (start with `Game/scenes/arena_02.tscn`'s `Environment_nebula`, then apply consistently across `arena_01`/`arena_03` too) currently have no post-processing. Enable and tune Glow (bloom) so the nebula core, emissive accent strips on the station model, and bright stars actually bleed light; enable Adjustments (`adjustment_enabled`) for a subtle contrast/saturation grade. Godot's `Environment` has no built-in vignette property — if that's still wanted, it needs a small custom full-screen shader (a `CompositorEffect` or a screen-space `ColorRect` overlay), not a toggle; treat it as a separate, smaller sub-task rather than assuming it's free. Also enable FXAA and/or TAA via `project.godot`'s `rendering/anti_aliasing/quality/*` settings project-wide to fix the aliased hard edges visible on ship geometry. Motion blur and depth-of-field are deliberately out of scope here — Godot has no built-in equivalent, and faking either well needs a custom `CompositorEffect`, which is a much bigger task than this pass. Verify with before/after screenshots via godot-mcp (`run_project` on `free_play.tscn` with the Nebula arena selected) — don't just eyeball the editor, actually run the game."
 
-- [ ] **De-duplicate the nebula sky's star sprites**. Every bright star in `sky_nebula.png` is the exact same diffraction-spike stamp at the same size/brightness, just relocated — called out as "the single most amateur-looking tell in the whole scene" once you look for more than a second.
+- [x] **De-duplicate the nebula sky's star sprites**. Every bright star in `sky_nebula.png` is the exact same diffraction-spike stamp at the same size/brightness, just relocated — called out as "the single most amateur-looking tell in the whole scene" once you look for more than a second. Fixed: the generator is now committed at `tools/textures/gen_nebula_sky.py`; the hero-star loop randomizes rotation, arm count (4 or 8), spike length, and brightness per star, and `sky_nebula.png` was regenerated/reimported and confirmed via in-game screenshot.
   Prompt: "Commit the nebula sky texture generator (currently only in an ephemeral scratchpad — recreate it if needed: numpy/Pillow script generating a 4096x2048 equirect nebula via layered FFT/domain-warped noise, color-graded, with drawn hero stars) into the repo at `tools/textures/gen_nebula_sky.py`. Fix the hero-star drawing loop so each star's diffraction-spike stamp gets randomized rotation, spike length, and brightness instead of reusing one identical stamp at every location. Regenerate `Game/assets/textures/sky_nebula.png`, reimport, and confirm via an in-game screenshot that the repeated-stamp tell is gone."
 
 - [ ] **Real PBR lighting + materials, fresnel glass boundary** (no new models — material/lighting setup only). Everything is flat-shaded/unshaded with a single directional light: no GI, no reflections, no bounce/AO, and the "glass" boundary is a flat unshaded tinted overlay with no fresnel rim or reflection.