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)

tests/run_all.sh

@@ -4,7 +4,7 @@
 # Usage: tests/run_all.sh   (from the repo root; needs `godot` on PATH)
 cd "$(dirname "$0")/.." || exit 1
 status=0
-for t in test_survival_core test_survival_stats test_save_load test_weather_building test_creatures_combat test_wolves test_fishing_diet test_net_lobby test_terrain_edges test_boundary; do
+for t in test_survival_core test_survival_stats test_save_load test_weather_building test_creatures_combat test_wolves test_fishing_diet test_net_lobby test_net_world test_terrain_edges test_boundary; do
 	extra=""
 	[ "$t" = "test_boundary" ] && extra="--fixed-fps 30"
 	# A suite that waits on a world that failed to load would hang forever,