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

tests/runner.gd

@@ -15,7 +15,7 @@ func _init():
 	print("1..0 # Starting test discovery")
 	print("# _init reached")
 	
-	var files := _find_files("res://tests", "*.gd", ["runner.gd"])
+	var files := _find_files("res://tests", "*.gd", ["runner.gd", "headless_test_bot.gd", "bot_test_scene.gd"])
 	print("# Found %d test file(s)" % files.size())
 
 	var total := 0