Remove Apex Dynamics faction, retune bullet speed/size

Drop Apex Dynamics from the playable roster (2 races now: Inner Sphere
Navy, Outer Rim Collective) to simplify the 2D art pipeline; World's
race-offer logic just shuffles both remaining races instead of picking
2 of N. Also fix bullets using a constant muzzle velocity instead of
adding the shooter's own velocity, and shrink the bullet hitbox/sprite.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

overview/structure.md

@@ -104,7 +104,7 @@ Player (CharacterBody2D)   ← ship_movement.gd
 ```
 main_menu.tscn
   ├── QUICK PLAY → matchmaking queue (casual) → world.tscn
-  │     ├── TeamSelect overlay: pick race (2 random of 3 offered)
+  │     ├── TeamSelect overlay: pick race (both offered every match)
   │     ├── TeamSelect overlay: pick ship
   │     └── Player spawns → game live
   ├── SERVER SELECT → server_select.tscn → pick a server → world.tscn (same TeamSelect flow)