Add engine flames, damage numbers, nameplates, music, and combat/collision fixes

Feature work (CLAUDE.md items 17-18):
- Race roster art rework (Apex/ISN/ORC) plus per-ship engine-flame sprites
  that swap in on thrust
- Floating damage-number VFX, per-ship nameplates, energy bar rework
- Background music manager and per-race ship SFX

Bugfixes/tuning from live testing:
- No friendly fire: bullets stop on a teammate's hull but deal no damage
  (bullet.gd), decided by race via PlayerRegistry
- Ships no longer physically block each other (own collision layer,
  ship.tscn/bullet.tscn) -- fixes ramming/parking trolling and the stuck-on-
  corpse bug after a kill
- Explosions ghost any ship's sprite passing through instead of blocking it
  (effects/explosion.gd's GhostArea)
- Fixed two "flushing physics queries" crashes from the above: explosion
  spawn and death/respawn collision toggling are now deferred
  (ship_movement.gd)
- Dead ships stop blocking bullets during their respawn delay
- Bots fly a mixed roster (1 Tank + 2 Gunner + rest Fighter per team)
  instead of always the Fighter (bot_manager.gd)
- Camera zoom knob, larger/longer-lived damage numbers and nameplate text,
  red (not yellow) enemy name color for better contrast

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

spacewar/menu/server_select.gd

@@ -37,6 +37,7 @@ var _ping_probes: Array = []  # {udp: PacketPeerUDP, start_msec: int, done: bool
 
 func _ready() -> void:
 	_build_ui()
+	MusicManager.play_menu_music()
 	NetworkManager.connection_succeeded.connect(_on_connected)
 	NetworkManager.connection_failed.connect(_on_connect_failed)
 	_refresh_servers()