Fix world population race and add multiplayer diagnostics

The world was populated before NetworkManager.world_ready() actually
called host()/join(), so owns_world() read true for every peer
(including a joining client) and each one built its own local,
unreplicated copy instead of the client receiving the server's spawn
through the MultiplayerSpawner. Population now happens after the
session is actually established.

Also adds net-log coverage for spawn/despawn, station gating, item
authority handoff, station snapping, avatar spawn/despawn, and scene
transitions, so multiplayer behavior is visible in
%TEMP%\vryhungry_net_<pid>.log instead of failing silently.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Net/net_pickable.gd

@@ -61,6 +61,8 @@ func _on_picked_up(_p) -> void:
 	var by := _pickable.get_picked_up_by()
 	if not (by is XRToolsFunctionPickup):
 		return
+	if NetworkManager.is_online():
+		NetworkManager.log_line("Grabbed %s by hand, requesting authority" % _pickable.name)
 	NetworkManager.request_item_authority.rpc_id(1, _pickable.get_path())
 
 
@@ -69,6 +71,8 @@ func _on_dropped(_p) -> void:
 	# apply_held_state() losing authority (see above) must not re-report.
 	if not is_multiplayer_authority():
 		return
+	if NetworkManager.is_online():
+		NetworkManager.log_line("Dropped %s, reporting release to server" % _pickable.name)
 	NetworkManager.release_item_authority.rpc_id(
 		1, _pickable.get_path(), _pickable.linear_velocity, _pickable.angular_velocity
 	)