Rebuild multiplayer on the stock spawner and synchronizer

Adding an object to the game no longer requires any networking code. The
MultiplayerSpawner runs in its default mode — no spawn_function, no payload
dictionary — and NetReplication builds each object's SceneReplicationConfig
from a convention, so scenes carry no hand-authored replication at all.

Every replicated node gets two generated synchronizers: NetSync for script
state, always server-owned, and NetXform for position, handed to whoever is
holding the object. That split is what makes grab prediction work — a
synchronizer never applies inbound state on the peer that owns it, so a
player's own hand drives an object with no round trip while is_dirty and
friends keep flowing one way from the server.

Interaction is now two RPCs for the whole game (NetGrab), and client gating is
one rule applied to every object (NetWorld). Deleted: net_pickable.gd, the
replicated net_held_by field and its held-state juggling, the
grant/reject/force-release negotiation, the static-item despawn RPC, and the
per-scene replication configs. Authority is the single source of truth for who
simulates an object.

Two things the convention had to learn, both found by the test suite:

  * Addon scripts are excluded. godot-xr-tools' snap zones and pickables expose
    a public `enabled`, which is exactly the flag each peer must set for itself
    — so replicating it meant the server sent `enabled = true` back over every
    client's gate, and stations went on grabbing objects out of the local
    player's hands.
  * Arrays of nodes are excluded. Array[Node3D] and Array[FoodItem] would
    otherwise try to serialise live node references.

table.gd's replicated state loses its underscore prefix, which now marks a
variable as private and unreplicated; two in-place array mutations there were
skipping their setters, and the progress bar could divide by zero on a client.

Suite: 146/146 passing.

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

Containers/container.gd

@@ -154,19 +154,22 @@ func refresh_visuals(ids: Array[String]) -> void:
 		visual.rotation = positions[idx].rotation
 
 
-# Strip interactivity/networking from a display-only copy: it's not spawned
-# through NetworkManager, so it must never try to sync (its NetPickable child,
-# if any, would have no corresponding replicated identity on other peers) or
-# be grabbable/collidable.
+# Strip interactivity from a display-only copy. It is instantiated straight from
+# its scene rather than spawned through NetWorld, so it is not part of the
+# replicated world at all — it exists only to be looked at, and must not be
+# grabbable or collidable.
+#
+# It gets no synchronizers either: NetReplication.attach only ever runs for
+# direct children of the content root, and this is parented under a plate.
 func _make_cosmetic(visual: Node3D) -> void:
-	var net_pickable := visual.get_node_or_null("NetPickable")
-	if net_pickable:
-		# Detach and free it outright rather than queue_free(): this runs before
+	var despawn_timer := visual.get_node_or_null("DespawningItem")
+	if despawn_timer:
+		# Detached and freed outright rather than queue_free()d: this runs before
 		# `visual` is added to the tree, and a merely-queued node still enters the
-		# tree with its parent and runs _ready() (which starts syncing and logging)
-		# before the queued deletion lands at the end of the frame.
-		visual.remove_child(net_pickable)
-		net_pickable.free()
+		# tree with its parent and runs a frame of _process before the queued
+		# deletion lands at the end of the frame.
+		visual.remove_child(despawn_timer)
+		despawn_timer.free()
 	if visual is RigidBody3D:
 		visual.freeze = true
 		# STATIC, not KINEMATIC: a kinematic body is still driven by the physics
@@ -193,9 +196,6 @@ func _make_cosmetic(visual: Node3D) -> void:
 func _remove_from_physics(visual: Node3D) -> void:
 	if visual is RigidBody3D:
 		PhysicsServer3D.body_set_space((visual as RigidBody3D).get_rid(), RID())
-		var despawning_item = visual.get_node_or_null("DespawningItem")
-		if despawning_item:
-			NetworkManager.despawn_item(despawning_item)
 
 
 #plate (Pickalbe)