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

assets/kenney-fps/weapons/blaster-repeater.tres

@@ -0,0 +1,16 @@
+[gd_resource type="Resource" script_class="Weapon" load_steps=4 format=3 uid="uid://cu2gtxlcmbb34"]
+
+[ext_resource type="Texture2D" uid="uid://ce3lgq7foiusl" path="res://sprites/crosshair-repeater.png" id="1_hoqei"]
+[ext_resource type="Script" uid="uid://dg01pkkc1c5vd" path="res://scripts/weapon.gd" id="1_l1atd"]
+[ext_resource type="PackedScene" uid="uid://dd3oln1ucgqpd" path="res://models/blaster-repeater.glb" id="2_h64nv"]
+
+[resource]
+script = ExtResource("1_l1atd")
+model = ExtResource("2_h64nv")
+rotation = Vector3(0, 180, 0)
+muzzle_position = Vector3(0.1, -0.4, 1.5)
+damage = 10.0
+spread = 0.5
+knockback = 10
+sound_shoot = "sounds/blaster_repeater.ogg"
+crosshair = ExtResource("1_hoqei")

assets/kenney-fps/weapons/blaster.tres

@@ -0,0 +1,19 @@
+[gd_resource type="Resource" script_class="Weapon" load_steps=4 format=3 uid="uid://c56y8pqoyk15f"]
+
+[ext_resource type="Texture2D" uid="uid://2jld33y6h5pq" path="res://sprites/crosshair.png" id="1_2onsr"]
+[ext_resource type="PackedScene" uid="uid://b2p7bbkuxf7m" path="res://models/blaster.glb" id="1_x0glg"]
+[ext_resource type="Script" uid="uid://dg01pkkc1c5vd" path="res://scripts/weapon.gd" id="2_107w7"]
+
+[resource]
+script = ExtResource("2_107w7")
+model = ExtResource("1_x0glg")
+rotation = Vector3(0, 180, 0)
+muzzle_position = Vector3(0.1, -0.4, 1.5)
+cooldown = 0.25
+spread = 1.0
+shot_count = 3
+knockback = 40
+min_knockback = Vector2(0.025, 0.025)
+max_knockback = Vector2(0.045, 0.04)
+sound_shoot = "sounds/blaster.ogg"
+crosshair = ExtResource("1_2onsr")