feat: Sketchfab-to-game character pipeline, FP/TP animated views, client-auth netcode, audio system

Character pipeline (tools/):
- sketchfab_import.py: search/download via Sketchfab Download API with
  license/attribution tracking (SKETCHFAB_API_TOKEN)
- autorig.py: headless Blender auto-rig — fits a Mixamo-named skeleton
  to unrigged humanoids, binds automatic weights
- merge_animations.py: merges the shared Mixamo-skeleton animation
  library onto any rigged character, strips root motion, canonical names
- pipeline.py: one command chains download -> rig -> animate -> register

In-game skin system:
- SkinManager autoload reads skins.json (auto-written by the pipeline)
- SkinnedPlayerModel rewritten: canonical clips with fallback chains,
  blend times, speed-scaled locomotion, weapon bone attachment
- First-person: full animated body for the owner, head hidden via
  SkeletonModifier3D; third-person: full model for other players
- Skin selector in main menu; skin id synced in multiplayer
- Fixed GLBLoader crash (GLTFDocument.get_animation_count doesn't exist)

Multiplayer sync overhaul:
- Movement is now client-authoritative: the owning peer simulates
  locally (no input round-trip), server keeps health/kills/death
- Remote players interpolate synced_position/velocity with
  extrapolation and snap-on-teleport
- Knockback/impulses routed to the simulating peer

Audio:
- AudioManager autoload: SFX/Weapons/Footsteps/UI/Music buses, pooled
  3D players, variation + pitch randomization, auto-registration from
  assets/sounds

Docs: 3D_ASSET_PIPELINE.md rewritten end-to-end, new ASSET_SOURCES.md
(non-procedural animation/map/sound sources) and SOUND_DESIGN.md.
Verified with debug/spawn_smoke_test.gd (headless: 24/24 checks pass).

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

project.godot

@@ -12,7 +12,7 @@ config_version=5
 
 config/name="Papaya-Shooter"
 run/main_scene="res://ui/main_menu/main_menu.tscn"
-config/features=PackedStringArray("4.6", "Forward Plus")
+config/features=PackedStringArray("4.7", "Forward Plus")
 config/icon="res://icon.svg"
 
 [autoload]
@@ -21,6 +21,8 @@ SettingsManager="*res://globals/settings_manager.gd"
 LoadoutManager="*res://globals/loadout_manager.gd"
 PauseMenu="*res://ui/pause_menu.gd"
 NetworkManager="*res://globals/network_manager.gd"
+SkinManager="*res://characters/skin_manager.gd"
+AudioManager="*res://globals/audio_manager.gd"
 
 [display]