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]>

debug/visual_capture.gd

@@ -0,0 +1,37 @@
+extends SceneTree
+
+## Dev tool: launch with rendering, screenshot the main menu and a level,
+## then quit. Run:
+##   godot --path . -s res://debug/visual_capture.gd -- <output_dir>
+## Screenshots land in <output_dir>/shot_menu.png and shot_level.png.
+
+var _frames := 0
+var _out_dir := "."
+
+
+func _initialize() -> void:
+	var args := OS.get_cmdline_user_args()
+	if args.size() > 0:
+		_out_dir = args[0]
+	change_scene_to_file("res://ui/main_menu/main_menu.tscn")
+
+
+func _process(_delta: float) -> bool:
+	_frames += 1
+	if _frames == 60:
+		_shot("menu")
+		var nm = root.get_node_or_null("NetworkManager")
+		if nm and nm.has_method("start_singleplayer_match"):
+			nm.start_singleplayer_match("Deathmatch")
+		change_scene_to_file("res://scenes/maps/test_level/test_level.tscn")
+	elif _frames == 240:
+		_shot("level")
+		return true
+	return false
+
+
+func _shot(tag: String) -> void:
+	var img := root.get_viewport().get_texture().get_image()
+	var path := _out_dir + "/shot_" + tag + ".png"
+	img.save_png(path)
+	print("visual_capture: saved ", path)