M2.2: player bodies, name tags, shared island and checked movement

- Joining loads the server's island (seed, spawn, clock); the server
  generates the same terrain from its seed and keeps a world clock that
  pauses when empty
- Other players are procedural low-poly characters in their chosen colours
  with name tags (hidden by walls, fading with distance), walk/run/swim
  animation and held items
- Movement: local and instant, sent at 20 Hz stamped with the sender's
  clock; the server refuses impossible moves (speed, rising, leaving the
  island, underground) and sends the player back; flagged respawns allowed
- Avatars drawn 100 ms behind and interpolated, with brief extrapolation
- Online: no pausing, player list in the Esc menu, Disconnect back to the
  title (with the reason); animals off and world changes local-only until
  M2.3-M2.5, shown on the HUD
- test_net_world: real server + walking and cheating bots at 100 ms +/-
  30 ms simulated latency (27 checks)

scripts/world/terrain.gd

@@ -69,9 +69,13 @@ var _heights := PackedFloat32Array()
 var _normals := PackedVector3Array()
 
 func _ready() -> void:
-	# A saved world brings its own seed; otherwise keep the exported default.
+	# On a server, its seed; in a saved world, that world's seed; otherwise
+	# keep the exported default.
+	var net := get_node_or_null("/root/Net")
 	var saves := get_node_or_null("/root/Saves")
-	if saves != null and saves.has_world():
+	if net != null and net.state == "connected" and net.world_info.has("seed"):
+		noise_seed = int(net.world_info.seed)
+	elif saves != null and saves.has_world():
 		noise_seed = saves.world_seed()
 	_build()