feat: cel-shaded look & feel overhaul — real audio, comic UI, themed VFX

Audio (all CC0 — Kenney packs + OpenGameArt, see assets/sounds/SOURCES.md):
- Replace every procedural synth WAV with forged sounds (ffmpeg pitch/layer
  mixes): distinct fire sounds per weapon with 2-3 variations, explosions,
  footsteps x5, land/jump/dash/vault, knife swing, hit/kill confirms,
  bullet impacts, reload, flight loops, UI hover/click/confirm/error,
  match jingles, menu music
- AudioManager.stream_for(): AudioStreamRandomizer per sound id — every
  weapon now gets variation + pitch randomization on each shot
- Explosions and bullet impacts play positional audio; landing has its own
  sound instead of a pitched footstep; ambient wind bed on every map

Visuals:
- ExplosionVFX: shared cel-shaded burst (white-hot stepped core, ink
  shockwave ring, star spikes, flat smoke puffs) replaces the orange
  sphere in both local and remote-replay paths
- Comic star muzzle flashes on all weapons; unified cel tracer bolts with
  ink outlines across hitscan/shotgun/remote paths
- Impact decals: hard-stepped ink-splat gradients instead of soft airbrush
- Toon shading on first-person view models + arms, third-person weapons,
  and the procedural humanoid fallback (no hull outlines on FBX weapons —
  their hard normals tear the inverted hull)
- Fix: giant soft "blob" highlight on floors — toon rim/specular disabled
  on level-geometry materials (pre-existing artifact since the cel commit)
- Fix: own third-person weapon rendered into the first-person camera
  (shadows-only now covers first_person_mode)

UI:
- UITheme: comic theme on the root window — Bangers display font (OFL),
  paper panels with thick ink borders + hard drop shadows, papaya accent,
  themed buttons/inputs/popups; hover/click sounds on all menu buttons
- Main menu: tilted comic wordmark, sunset toon diorama, looping menu music
- Match HUD: themed scoreboard/killfeed/kill counter

Viewports:
- 4x MSAA project-wide + viewmodel/diorama viewports (crisp ink lines)
- Viewmodel camera near plane 0.01; third-person camera FOV syncs settings
- debug/visual_capture.gd: dev tool to screenshot menu + level for review

Verified: 11/11 movement tests, spawn smoke test 0 failures, before/after
screenshot comparison of menu and level.

Co-Authored-By: Claude Fable 5 <[email protected]>

weapons/explosive_projectile.gd

@@ -210,35 +210,5 @@ func _explode(pos: Vector3) -> void:
 	if owner_player and owner_player.is_multiplayer_authority() and owner_player.has_method("server_play_explosion") and owner_player.multiplayer.has_multiplayer_peer() and not(owner_player.multiplayer.multiplayer_peer is OfflineMultiplayerPeer):
 		owner_player.server_play_explosion.rpc_id(1, pos, explosion_radius)
 		
-	# Local Visual Effect
-	var visual = MeshInstance3D.new()
-	var s_mesh = SphereMesh.new()
-	s_mesh.radius = explosion_radius
-	s_mesh.height = explosion_radius * 2.0
-	visual.mesh = s_mesh
-	
-	var mat = StandardMaterial3D.new()
-	mat.albedo_color = Color(1.0, 0.5, 0.0, 0.6) # Translucent orange
-	mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
-	mat.emission_enabled = true
-	mat.emission = Color(1.0, 0.3, 0.0)
-	visual.material_override = mat
-	
-	visual.position = pos
-	get_tree().current_scene.add_child(visual)
-	
-	var tween = visual.create_tween()
-	tween.tween_property(mat, "albedo_color:a", 0.0, 0.3)
-	tween.parallel().tween_property(visual, "scale", Vector3(1.1, 1.1, 1.1), 0.3)
-	tween.tween_callback(visual.queue_free)
-	
-	# Audio Effect
-	var audio = AudioStreamPlayer3D.new()
-	audio.stream = load("res://assets/sounds/shotgun_fire.wav") # using shotgun fire for a crash explosion
-	audio.bus = "SFX"
-	audio.pitch_scale = explosion_pitch
-	audio.max_distance = 150.0
-	get_tree().current_scene.add_child(audio)
-	audio.global_position = pos
-	audio.play()
-	audio.finished.connect(audio.queue_free)
+	# Local visual + audio: shared cel-shaded burst (also used by remote replay)
+	ExplosionVFX.spawn(get_tree(), pos, explosion_radius)