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/impact_spawner.gd

@@ -19,7 +19,9 @@ static func _ensure_mats():
 		for c in colors: p_colors.append(c)
 		g.offsets = p_offsets
 		g.colors = p_colors
-		
+		# Hard color steps: reads as inked cel splats instead of soft airbrush
+		g.interpolation_mode = Gradient.GRADIENT_INTERPOLATE_CONSTANT
+
 		var t = GradientTexture2D.new()
 		t.gradient = g
 		t.fill = GradientTexture2D.FILL_RADIAL
@@ -62,6 +64,12 @@ static func _ensure_mats():
 
 static func spawn(scene_tree: SceneTree, type: String, pos: Vector3, normal: Vector3, size: float = 0.2):
 	_ensure_mats()
+
+	# Positional impact tick (pooled; safe at fire-rate frequency)
+	if type == "bullet":
+		var am = scene_tree.root.get_node_or_null("AudioManager")
+		if am and am.has_sound("bullet_impact"):
+			am.play_3d("bullet_impact", pos, -6.0)
 	
 	var mi = MeshInstance3D.new()
 	var qm = QuadMesh.new()