Avatars actually show; camera stops hugging the player

- SpringArm3D was colliding with the player's own capsule (same layer) ->
  camera yanked up against the head. add_excluded_object(self) in _ready +
  gentler default pitch, shorter arm, lower pivot.
- AvatarSystem.build_current_avatar() is now self-sufficient: loads the
  catalog itself and falls back to a bare default loadout if login didn't
  prime one. So the in-world player always shows an avatar, never the
  capsule, as long as the assets are packed (they are now).
- New AvatarSystem.assemble_avatar(): builds a standalone avatar with a
  throwaway loader, touching no shared state -- so it's safe to call once
  for the local player AND once per remote peer. (load_avatar()'s shared
  loader reset()s and freed the previous avatar on every call.)
- game.gd: remote players render as the assembled avatar too (shared default
  look, tinted per-peer, name tag) instead of a plain capsule.

Client-side -- rebuild the exe.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scenes/player.tscn

@@ -20,10 +20,10 @@ shape = SubResource("CapsuleShape1")
 mesh = SubResource("CapsuleMesh1")
 
 [node name="CameraPivot" type="Node3D" parent="."]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1.4, 0)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1.2, 0)
 
 [node name="SpringArm3D" type="SpringArm3D" parent="CameraPivot"]
-spring_length = 4.0
+spring_length = 3.5
 margin = 0.2
 
 [node name="Camera3D" type="Camera3D" parent="CameraPivot/SpringArm3D"]