Server launcher and start-up checks for other machines

- server/run_server.sh: checks Godot is 4.7+, imports a fresh copy once
  (the class cache in .godot/ isn't in git), then starts the server
- The dedicated server refuses to start, with a clear reason, on Godot
  older than 4.7 or when the game's scripts failed to load, instead of
  claiming to listen
- tests/run_all.sh imports a fresh copy first
- Setup doc: 4.7+ (not 4.3+), importing a fresh copy, running a server

tests/run_all.sh

@@ -4,6 +4,11 @@
 # Usage: tests/run_all.sh   (from the repo root; needs `godot` on PATH)
 cd "$(dirname "$0")/.." || exit 1
 status=0
+# A fresh clone has no class cache yet (.godot/ isn't in git): import once.
+if [ ! -f .godot/global_script_class_cache.cfg ]; then
+	echo "Importing the project first (fresh copy)..."
+	godot --headless --path . --import >/dev/null 2>&1
+fi
 for t in test_survival_core test_survival_stats test_save_load test_weather_building test_creatures_combat test_wolves test_fishing_diet test_net_lobby test_net_world test_terrain_edges test_boundary; do
 	extra=""
 	[ "$t" = "test_boundary" ] && extra="--fixed-fps 30"