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/fonts/lilita_one_regular.ttf.import

@@ -0,0 +1,36 @@
+[remap]
+
+importer="font_data_dynamic"
+type="FontFile"
+uid="uid://ck0qqay65t74q"
+path="res://.godot/imported/lilita_one_regular.ttf-3dca4fa94079006a715a4d35e33d3f68.fontdata"
+
+[deps]
+
+source_file="res://assets/kenney/fonts/lilita_one_regular.ttf"
+dest_files=["res://.godot/imported/lilita_one_regular.ttf-3dca4fa94079006a715a4d35e33d3f68.fontdata"]
+
+[params]
+
+Rendering=null
+antialiasing=1
+generate_mipmaps=false
+disable_embedded_bitmaps=true
+multichannel_signed_distance_field=false
+msdf_pixel_range=8
+msdf_size=48
+allow_system_fallback=true
+force_autohinter=false
+modulate_color_glyphs=false
+hinting=3
+subpixel_positioning=4
+keep_rounding_remainders=true
+oversampling=0.0
+Fallbacks=null
+fallbacks=[]
+Compress=null
+compress=true
+preload=[]
+language_support={}
+script_support={}
+opentype_features={}