feat: add post-processing pass and video settings menu

Enable glow/bloom, color adjustments, and MSAA+FXAA across all three
arenas so emissive ship/station accents actually bleed light and edges
read cleanly. Expose the player-facing knobs (anti-aliasing mode, glow
intensity, brightness) through a new Settings screen off the main menu,
persisted via a VideoSettings autoload that scales each arena's own
tuned Environment values on load rather than overwriting them.

Game/project.godot

@@ -116,7 +116,12 @@ roll_right={
 common/physics_interpolation=true
 3d/physics_engine="Jolt Physics"
 
+[rendering]
+
+anti_aliasing/quality/msaa_3d=2
+anti_aliasing/quality/screen_space_aa=1
+
 [autoload]
 
-
 GameSettings="*res://scripts/game_settings.gd"
+VideoSettings="*res://scripts/video_settings.gd"