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)

docs/SETUP_ON_NEW_MACHINE.md

@@ -38,6 +38,8 @@ godot --headless --path . --script res://tests/test_survival_core.gd
 godot --headless --path . --script res://tests/test_save_load.gd
 # Multiplayer lobby: a real headless server on UDP 24343 + scripted bot players
 godot --headless --path . --script res://tests/test_net_lobby.gd
+# Multiplayer world: avatars, smooth movement at 100 ms latency, cheat checks (UDP 24345)
+godot --headless --path . --script res://tests/test_net_world.gd
 # Survival stats: hunger, warmth, fire fuel, cooking, foraging, death + grave
 godot --headless --path . --script res://tests/test_survival_stats.gd
 ```