Integrate Kenney Starter Kit FPS assets + comprehensive test suite

Assets (CC0 license):
- 3D models: Blaster gun, walls, platforms, grass, clouds, enemy
- Sounds: blaster fire, impacts, footsteps, jumps, weapon change
- Sprites: crosshair, hit marker, muzzle flash, skybox, blob shadow
- Font: Lilita One

Code changes:
- weapon_manager.gd: load blaster.glb as gun model (replaces box mesh)
- player.tscn: use Kenney sounds (blaster.ogg, enemy_hurt/destroy) and crosshair

Test suite (100 unit tests + 4 integration scenarios):
- weapon_data.gd: 27 tests — all 6 weapons every stat verified
- economy.gd: 19 tests — constants, loss streak, buy thresholds
- bomb.gd: 15 tests — state machine, timing constants
- round_manager.gd: 10 tests — win conditions, elimination logic
- team_manager.gd: 8 tests — auto-balance, team assignment
- headless_test_bot.gd: integration bot with movement/idle/rounds scenarios
- run_multi_bot.sh: multi-client launcher

examples/multiplayer-fps/scripts/weapon_manager.gd

@@ -59,6 +59,20 @@ func _load_weapon_models():
 		add_child(_grenade_model)
 		_grenade_model.hide()
 
+	# Gun model — replace placeholder box with Kenney blaster
+	var gun_scene := load("res://assets/kenney/models/blaster.glb") as PackedScene
+	if gun_scene:
+		var blaster = gun_scene.instantiate()
+		blaster.scale = Vector3(0.003, 0.003, 0.003)
+		blaster.position = Vector3(0.09, -0.18, -0.3)
+		blaster.rotation_degrees = Vector3(-90, 180, 0)
+		add_child(blaster)
+		# Hide the old box mesh, use blaster instead
+		if _gun_model:
+			_gun_model.hide()
+		_gun_model = blaster
+		_gun_model.hide()
+
 	# Knife sound
 	var slash_stream := load("res://examples/multiplayer-fps/sounds/knife/knife_slash1.wav")
 	if slash_stream: